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 $53.49   12.368%   $60.1056   $60.11   $60.10   $60.10  
  Purchase #2 $212.26   8.594%   $230.5016   $230.50   $230.50   $230.50  
  Purchase #3 $23.42   7.750%   $25.2351   $25.24   $25.25   $25.20  
  Purchase #4 $182.71   4.498%   $190.9283   $190.93   $190.95   $190.90  
  Purchase #5 $247.88   10.124%   $272.9754   $272.98   $273.00   $273.00  
  Purchase #6 $95.66   3.686%   $99.186   $99.19   $99.20   $99.20  
  Purchase #7 $63.37   4.546%   $66.2508   $66.25   $66.25   $66.30  
  7 purchase totals = $878.79       $945.1828   $945.20   $945.25   $945.20