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 $50.62   13.546%   $57.477   $57.48   $57.50   $57.50  
  Purchase #2 $30.72   13.144%   $34.7578   $34.76   $34.75   $34.80  
  Purchase #3 $62.59   12.395%   $70.348   $70.35   $70.35   $70.30  
  Purchase #4 $245.97   5.717%   $260.0321   $260.03   $260.05   $260.00  
  Purchase #5 $133.25   6.324%   $141.6767   $141.68   $141.70   $141.70  
  Purchase #6 $15.45   6.140%   $16.3986   $16.40   $16.40   $16.40  
  Purchase #7 $119.68   10.642%   $132.4163   $132.42   $132.40   $132.40  
  7 purchase totals = $658.28       $713.1065   $713.12   $713.15   $713.10