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 $188.81   6.790%   $201.6302   $201.63   $201.65   $201.60  
  Purchase #2 $54.29   5.719%   $57.3948   $57.39   $57.40   $57.40  
  Purchase #3 $94.85   3.134%   $97.8226   $97.82   $97.80   $97.80  
  Purchase #4 $231.71   5.828%   $245.2141   $245.21   $245.20   $245.20  
  Purchase #5 $10.25   6.665%   $10.9332   $10.93   $10.95   $10.90  
  Purchase #6 $210.38   13.553%   $238.8928   $238.89   $238.90   $238.90  
  Purchase #7 $180.50   8.257%   $195.4039   $195.40   $195.40   $195.40  
  7 purchase totals = $970.79       $1,047.2916   $1,047.27   $1,047.30   $1,047.20