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 $243.35   5.588%   $256.9484   $256.95   $256.95   $256.90  
  Purchase #2 $70.66   12.603%   $79.5653   $79.57   $79.55   $79.60  
  Purchase #3 $227.87   8.804%   $247.9317   $247.93   $247.95   $247.90  
  Purchase #4 $94.95   13.133%   $107.4198   $107.42   $107.40   $107.40  
  Purchase #5 $81.48   13.114%   $92.1653   $92.17   $92.15   $92.20  
  Purchase #6 $54.43   8.852%   $59.2481   $59.25   $59.25   $59.20  
  Purchase #7 $158.64   3.778%   $164.6334   $164.63   $164.65   $164.60  
  7 purchase totals = $931.38       $1,007.9120   $1,007.92   $1,007.90   $1,007.80