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 $82.54   6.293%   $87.7342   $87.73   $87.75   $87.70  
  Purchase #2 $244.25   5.193%   $256.9339   $256.93   $256.95   $256.90  
  Purchase #3 $167.96   7.734%   $180.95   $180.95   $180.95   $181.00  
  Purchase #4 $76.66   9.723%   $84.1137   $84.11   $84.10   $84.10  
  Purchase #5 $236.83   10.651%   $262.0548   $262.05   $262.05   $262.10  
  Purchase #6 $9.49   13.530%   $10.774   $10.77   $10.75   $10.80  
  Purchase #7 $63.38   13.499%   $71.9357   $71.94   $71.95   $71.90  
  7 purchase totals = $881.11       $954.4963   $954.48   $954.50   $954.50