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 $215.47   12.268%   $241.9039   $241.90   $241.90   $241.90  
  Purchase #2 $17.82   7.322%   $19.1248   $19.12   $19.10   $19.10  
  Purchase #3 $143.44   4.317%   $149.6323   $149.63   $149.65   $149.60  
  Purchase #4 $245.53   4.761%   $257.2197   $257.22   $257.20   $257.20  
  Purchase #5 $83.51   11.300%   $92.9466   $92.95   $92.95   $92.90  
  Purchase #6 $130.37   4.594%   $136.3592   $136.36   $136.35   $136.40  
  Purchase #7 $153.68   11.716%   $171.6851   $171.69   $171.70   $171.70  
  7 purchase totals = $989.82       $1,068.8716   $1,068.87   $1,068.85   $1,068.80