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 $208.89   11.550%   $233.0168   $233.02   $233.00   $233.00  
  Purchase #2 $197.27   9.679%   $216.3638   $216.36   $216.35   $216.40  
  Purchase #3 $52.63   12.423%   $59.1682   $59.17   $59.15   $59.20  
  Purchase #4 $225.54   5.634%   $238.2469   $238.25   $238.25   $238.20  
  Purchase #5 $236.40   5.583%   $249.5982   $249.60   $249.60   $249.60  
  Purchase #6 $84.51   5.318%   $89.0042   $89.00   $89.00   $89.00  
  Purchase #7 $32.62   6.698%   $34.8049   $34.80   $34.80   $34.80  
  7 purchase totals = $1,037.86       $1,120.2030   $1,120.20   $1,120.15   $1,120.20