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 $62.43   12.443%   $70.1982   $70.20   $70.20   $70.20  
  Purchase #2 $169.38   11.634%   $189.0857   $189.09   $189.10   $189.10  
  Purchase #3 $111.89   11.712%   $124.9946   $124.99   $125.00   $125.00  
  Purchase #4 $154.38   12.531%   $173.7254   $173.73   $173.75   $173.70  
  Purchase #5 $49.70   12.176%   $55.7515   $55.75   $55.75   $55.80  
  Purchase #6 $28.46   3.447%   $29.441   $29.44   $29.45   $29.40  
  Purchase #7 $167.69   10.228%   $184.8413   $184.84   $184.85   $184.80  
  7 purchase totals = $743.93       $828.0377   $828.04   $828.10   $828.00