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 $29.93   7.341%   $32.1272   $32.13   $32.15   $32.10  
  Purchase #2 $58.91   10.761%   $65.2493   $65.25   $65.25   $65.20  
  Purchase #3 $235.49   9.446%   $257.7344   $257.73   $257.75   $257.70  
  Purchase #4 $164.63   6.752%   $175.7458   $175.75   $175.75   $175.70  
  Purchase #5 $197.49   4.785%   $206.9399   $206.94   $206.95   $206.90  
  Purchase #6 $74.50   7.315%   $79.9497   $79.95   $79.95   $79.90  
  Purchase #7 $171.61   11.755%   $191.7828   $191.78   $191.80   $191.80  
  7 purchase totals = $932.56       $1,009.5291   $1,009.53   $1,009.60   $1,009.30