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 $214.83   10.261%   $236.8737   $236.87   $236.85   $236.90  
  Purchase #2 $43.71   11.742%   $48.8424   $48.84   $48.85   $48.80  
  Purchase #3 $180.36   13.660%   $204.9972   $205.00   $205.00   $205.00  
  Purchase #4 $54.35   8.248%   $58.8328   $58.83   $58.85   $58.80  
  Purchase #5 $144.27   10.592%   $159.5511   $159.55   $159.55   $159.60  
  Purchase #6 $55.85   13.169%   $63.2049   $63.20   $63.20   $63.20  
  Purchase #7 $155.72   9.605%   $170.6769   $170.68   $170.70   $170.70  
  7 purchase totals = $849.09       $942.9790   $942.97   $943.00   $943.00