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 $104.61   11.390%   $116.5251   $116.53   $116.55   $116.50  
  Purchase #2 $151.79   9.839%   $166.7246   $166.72   $166.70   $166.70  
  Purchase #3 $44.26   3.179%   $45.667   $45.67   $45.65   $45.70  
  Purchase #4 $178.65   5.476%   $188.4329   $188.43   $188.45   $188.40  
  Purchase #5 $148.29   7.650%   $159.6342   $159.63   $159.65   $159.60  
  Purchase #6 $77.81   7.546%   $83.6815   $83.68   $83.70   $83.70  
  Purchase #7 $14.51   11.794%   $16.2213   $16.22   $16.20   $16.20  
  7 purchase totals = $719.92       $776.8866   $776.88   $776.90   $776.80