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 $231.61   12.342%   $260.1953   $260.20   $260.20   $260.20  
  Purchase #2 $62.51   6.785%   $66.7513   $66.75   $66.75   $66.80  
  Purchase #3 $155.46   11.348%   $173.1016   $173.10   $173.10   $173.10  
  Purchase #4 $177.42   11.489%   $197.8038   $197.80   $197.80   $197.80  
  Purchase #5 $89.78   3.549%   $92.9663   $92.97   $92.95   $93.00  
  Purchase #6 $190.69   9.125%   $208.0905   $208.09   $208.10   $208.10  
  Purchase #7 $179.97   8.287%   $194.8841   $194.88   $194.90   $194.90  
  7 purchase totals = $1,087.44       $1,193.7929   $1,193.79   $1,193.80   $1,193.90