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 $44.81   12.569%   $50.4422   $50.44   $50.45   $50.40  
  Purchase #2 $156.49   6.314%   $166.3708   $166.37   $166.35   $166.40  
  Purchase #3 $243.49   13.652%   $276.7313   $276.73   $276.75   $276.70  
  Purchase #4 $95.51   5.817%   $101.0658   $101.07   $101.05   $101.10  
  Purchase #5 $245.99   11.642%   $274.6282   $274.63   $274.65   $274.60  
  Purchase #6 $100.56   4.618%   $105.2039   $105.20   $105.20   $105.20  
  Purchase #7 $39.91   5.162%   $41.9702   $41.97   $41.95   $42.00  
  7 purchase totals = $926.76       $1,016.4124   $1,016.41   $1,016.40   $1,016.40