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 $236.96   11.858%   $265.0587   $265.06   $265.05   $265.10  
  Purchase #2 $122.77   7.812%   $132.3608   $132.36   $132.35   $132.40  
  Purchase #3 $59.78   3.751%   $62.0223   $62.02   $62.00   $62.00  
  Purchase #4 $112.49   3.761%   $116.7207   $116.72   $116.70   $116.70  
  Purchase #5 $217.56   8.681%   $236.4464   $236.45   $236.45   $236.40  
  Purchase #6 $97.69   3.492%   $101.1013   $101.10   $101.10   $101.10  
  Purchase #7 $51.28   10.748%   $56.7916   $56.79   $56.80   $56.80  
  7 purchase totals = $898.53       $970.5018   $970.50   $970.45   $970.50