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 $59.44   12.691%   $66.9835   $66.98   $67.00   $67.00  
  Purchase #2 $241.90   7.597%   $260.2771   $260.28   $260.30   $260.30  
  Purchase #3 $29.49   13.531%   $33.4803   $33.48   $33.50   $33.50  
  Purchase #4 $101.84   10.287%   $112.3163   $112.32   $112.30   $112.30  
  Purchase #5 $62.44   7.841%   $67.3359   $67.34   $67.35   $67.30  
  Purchase #6 $90.55   3.809%   $93.999   $94.00   $94.00   $94.00  
  Purchase #7 $215.61   10.155%   $237.5052   $237.51   $237.50   $237.50  
  7 purchase totals = $801.27       $871.8973   $871.91   $871.95   $871.90