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 $56.44   13.584%   $64.1068   $64.11   $64.10   $64.10  
  Purchase #2 $65.95   4.152%   $68.6882   $68.69   $68.70   $68.70  
  Purchase #3 $10.88   13.103%   $12.3056   $12.31   $12.30   $12.30  
  Purchase #4 $120.59   4.140%   $125.5824   $125.58   $125.60   $125.60  
  Purchase #5 $26.60   7.475%   $28.5884   $28.59   $28.60   $28.60  
  Purchase #6 $246.29   12.322%   $276.6379   $276.64   $276.65   $276.60  
  Purchase #7 $206.29   6.136%   $218.948   $218.95   $218.95   $218.90  
  7 purchase totals = $733.04       $794.8573   $794.87   $794.90   $794.80