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 $177.33   10.337%   $195.6606   $195.66   $195.65   $195.70  
  Purchase #2 $241.92   5.260%   $254.645   $254.65   $254.65   $254.60  
  Purchase #3 $146.38   4.809%   $153.4194   $153.42   $153.40   $153.40  
  Purchase #4 $156.48   6.870%   $167.2302   $167.23   $167.25   $167.20  
  Purchase #5 $223.40   13.872%   $254.39   $254.39   $254.40   $254.40  
  Purchase #6 $156.86   12.537%   $176.5255   $176.53   $176.55   $176.50  
  Purchase #7 $111.41   12.473%   $125.3062   $125.31   $125.30   $125.30  
  7 purchase totals = $1,213.78       $1,327.1769   $1,327.19   $1,327.20   $1,327.10