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 $212.77   7.375%   $228.4618   $228.46   $228.45   $228.50  
  Purchase #2 $119.39   13.428%   $135.4217   $135.42   $135.40   $135.40  
  Purchase #3 $209.91   12.344%   $235.8213   $235.82   $235.80   $235.80  
  Purchase #4 $15.29   4.533%   $15.9831   $15.98   $16.00   $16.00  
  Purchase #5 $112.96   3.191%   $116.5646   $116.56   $116.55   $116.60  
  Purchase #6 $27.51   4.163%   $28.6552   $28.66   $28.65   $28.70  
  Purchase #7 $83.32   10.200%   $91.8186   $91.82   $91.80   $91.80  
  7 purchase totals = $781.15       $852.7263   $852.72   $852.65   $852.80