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 $179.66   12.399%   $201.936   $201.94   $201.95   $201.90  
  Purchase #2 $141.74   12.137%   $158.943   $158.94   $158.95   $158.90  
  Purchase #3 $59.52   4.166%   $61.9996   $62.00   $62.00   $62.00  
  Purchase #4 $60.93   12.179%   $68.3507   $68.35   $68.35   $68.40  
  Purchase #5 $127.29   12.577%   $143.2993   $143.30   $143.30   $143.30  
  Purchase #6 $191.85   12.862%   $216.5257   $216.53   $216.55   $216.50  
  Purchase #7 $95.35   10.568%   $105.4266   $105.43   $105.45   $105.40  
  7 purchase totals = $856.34       $956.4809   $956.49   $956.55   $956.40