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 $249.49   8.736%   $271.2854   $271.29   $271.30   $271.30  
  Purchase #2 $51.37   3.825%   $53.3349   $53.33   $53.35   $53.30  
  Purchase #3 $38.60   9.200%   $42.1512   $42.15   $42.15   $42.20  
  Purchase #4 $184.56   12.857%   $208.2889   $208.29   $208.30   $208.30  
  Purchase #5 $59.92   6.827%   $64.0107   $64.01   $64.00   $64.00  
  Purchase #6 $214.27   12.814%   $241.7266   $241.73   $241.75   $241.70  
  Purchase #7 $174.81   11.798%   $195.4341   $195.43   $195.45   $195.40  
  7 purchase totals = $973.02       $1,076.2318   $1,076.23   $1,076.30   $1,076.20