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 $68.89   10.283%   $75.974   $75.97   $75.95   $76.00  
  Purchase #2 $141.98   6.196%   $150.7771   $150.78   $150.80   $150.80  
  Purchase #3 $16.29   4.767%   $17.0665   $17.07   $17.05   $17.10  
  Purchase #4 $34.68   5.328%   $36.5278   $36.53   $36.55   $36.50  
  Purchase #5 $125.28   13.108%   $141.7017   $141.70   $141.70   $141.70  
  Purchase #6 $57.66   8.597%   $62.617   $62.62   $62.60   $62.60  
  Purchase #7 $230.31   3.768%   $238.9881   $238.99   $239.00   $239.00  
  7 purchase totals = $675.09       $723.6522   $723.66   $723.65   $723.70