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 $44.79   7.229%   $48.0279   $48.03   $48.05   $48.00  
  Purchase #2 $236.25   11.511%   $263.4447   $263.44   $263.45   $263.40  
  Purchase #3 $12.84   4.680%   $13.4409   $13.44   $13.45   $13.40  
  Purchase #4 $95.42   13.655%   $108.4496   $108.45   $108.45   $108.40  
  Purchase #5 $67.85   5.522%   $71.5967   $71.60   $71.60   $71.60  
  Purchase #6 $186.54   5.369%   $196.5553   $196.56   $196.55   $196.60  
  Purchase #7 $64.31   5.747%   $68.0059   $68.01   $68.00   $68.00  
  7 purchase totals = $708.00       $769.5210   $769.53   $769.55   $769.40