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 $79.33   13.169%   $89.777   $89.78   $89.80   $89.80  
  Purchase #2 $210.80   3.120%   $217.377   $217.38   $217.40   $217.40  
  Purchase #3 $179.86   12.478%   $202.3029   $202.30   $202.30   $202.30  
  Purchase #4 $241.68   9.168%   $263.8372   $263.84   $263.85   $263.80  
  Purchase #5 $236.82   10.476%   $261.6293   $261.63   $261.65   $261.60  
  Purchase #6 $62.60   9.478%   $68.5332   $68.53   $68.55   $68.50  
  Purchase #7 $204.83   13.224%   $231.9167   $231.92   $231.90   $231.90  
  7 purchase totals = $1,215.92       $1,335.3733   $1,335.38   $1,335.45   $1,335.30