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 $236.41   12.738%   $266.5239   $266.52   $266.50   $266.50  
  Purchase #2 $55.93   6.711%   $59.6835   $59.68   $59.70   $59.70  
  Purchase #3 $125.39   5.405%   $132.1673   $132.17   $132.15   $132.20  
  Purchase #4 $245.43   11.699%   $274.1429   $274.14   $274.15   $274.10  
  Purchase #5 $120.64   3.590%   $124.971   $124.97   $124.95   $125.00  
  Purchase #6 $71.97   4.546%   $75.2418   $75.24   $75.25   $75.20  
  Purchase #7 $146.89   11.375%   $163.5987   $163.60   $163.60   $163.60  
  7 purchase totals = $1,002.66       $1,096.3291   $1,096.32   $1,096.30   $1,096.30