Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $137.71   11.126%   $153.0316   $153.03   $153.05   $153.00  
  Purchase #2 $174.40   10.319%   $192.3963   $192.40   $192.40   $192.40  
  Purchase #3 $214.35   12.595%   $241.3474   $241.35   $241.35   $241.30  
  Purchase #4 $129.71   8.221%   $140.3735   $140.37   $140.35   $140.40  
  Purchase #5 $146.68   11.854%   $164.0674   $164.07   $164.05   $164.10  
  Purchase #6 $143.56   12.292%   $161.2064   $161.21   $161.20   $161.20  
  Purchase #7 $230.27   9.566%   $252.2976   $252.30   $252.30   $252.30  
  7 purchase totals = $1,176.68       $1,304.7202   $1,304.73   $1,304.70   $1,304.70