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 $61.92   7.451%   $66.5337   $66.53   $66.55   $66.50  
  Purchase #2 $132.83   10.267%   $146.4677   $146.47   $146.45   $146.50  
  Purchase #3 $53.56   8.479%   $58.1014   $58.10   $58.10   $58.10  
  Purchase #4 $202.73   13.489%   $230.0762   $230.08   $230.10   $230.10  
  Purchase #5 $74.46   5.608%   $78.6357   $78.64   $78.65   $78.60  
  Purchase #6 $249.77   8.548%   $271.1203   $271.12   $271.10   $271.10  
  Purchase #7 $94.38   13.536%   $107.1553   $107.16   $107.15   $107.20  
  7 purchase totals = $869.65       $958.0903   $958.10   $958.10   $958.10