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 $224.60   13.267%   $254.3977   $254.40   $254.40   $254.40  
  Purchase #2 $125.82   3.475%   $130.1922   $130.19   $130.20   $130.20  
  Purchase #3 $177.58   12.731%   $200.1877   $200.19   $200.20   $200.20  
  Purchase #4 $189.98   7.749%   $204.7016   $204.70   $204.70   $204.70  
  Purchase #5 $82.67   10.414%   $91.2793   $91.28   $91.30   $91.30  
  Purchase #6 $10.86   10.211%   $11.9689   $11.97   $11.95   $12.00  
  Purchase #7 $78.53   4.820%   $82.3151   $82.32   $82.30   $82.30  
  7 purchase totals = $890.04       $975.0425   $975.05   $975.05   $975.10