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 $196.29   13.253%   $222.3043   $222.30   $222.30   $222.30  
  Purchase #2 $125.87   3.434%   $130.1924   $130.19   $130.20   $130.20  
  Purchase #3 $84.86   11.191%   $94.3567   $94.36   $94.35   $94.40  
  Purchase #4 $35.67   3.352%   $36.8657   $36.87   $36.85   $36.90  
  Purchase #5 $146.78   3.798%   $152.3547   $152.35   $152.35   $152.40  
  Purchase #6 $207.85   13.830%   $236.5957   $236.60   $236.60   $236.60  
  Purchase #7 $137.82   7.597%   $148.2902   $148.29   $148.30   $148.30  
  7 purchase totals = $935.14       $1,020.9597   $1,020.96   $1,020.95   $1,021.10