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 $56.48   9.540%   $61.8682   $61.87   $61.85   $61.90  
  Purchase #2 $138.91   7.633%   $149.513   $149.51   $149.50   $149.50  
  Purchase #3 $94.36   3.663%   $97.8164   $97.82   $97.80   $97.80  
  Purchase #4 $191.36   4.302%   $199.5923   $199.59   $199.60   $199.60  
  Purchase #5 $72.34   5.595%   $76.3874   $76.39   $76.40   $76.40  
  Purchase #6 $107.50   4.136%   $111.9462   $111.95   $111.95   $111.90  
  Purchase #7 $202.92   7.393%   $217.9219   $217.92   $217.90   $217.90  
  7 purchase totals = $863.87       $915.0454   $915.05   $915.00   $915.00