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 $84.69   13.562%   $96.1757   $96.18   $96.20   $96.20  
  Purchase #2 $158.62   11.445%   $176.7741   $176.77   $176.75   $176.80  
  Purchase #3 $63.95   3.829%   $66.3986   $66.40   $66.40   $66.40  
  Purchase #4 $69.65   9.299%   $76.1268   $76.13   $76.15   $76.10  
  Purchase #5 $141.49   12.282%   $158.8678   $158.87   $158.85   $158.90  
  Purchase #6 $5.85   12.512%   $6.582   $6.58   $6.60   $6.60  
  Purchase #7 $70.39   3.872%   $73.1155   $73.12   $73.10   $73.10  
  7 purchase totals = $594.64       $654.0405   $654.05   $654.05   $654.10