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 $243.69   3.136%   $251.3321   $251.33   $251.35   $251.30  
  Purchase #2 $6.95   5.340%   $7.3211   $7.32   $7.30   $7.30  
  Purchase #3 $152.99   5.553%   $161.4855   $161.49   $161.50   $161.50  
  Purchase #4 $42.38   8.775%   $46.0988   $46.10   $46.10   $46.10  
  Purchase #5 $180.96   8.109%   $195.634   $195.63   $195.65   $195.60  
  Purchase #6 $6.49   4.772%   $6.7997   $6.80   $6.80   $6.80  
  Purchase #7 $87.97   5.667%   $92.9553   $92.96   $92.95   $93.00  
  7 purchase totals = $721.43       $761.6265   $761.63   $761.65   $761.60