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 $55.44   12.467%   $62.3517   $62.35   $62.35   $62.40  
  Purchase #2 $209.68   12.585%   $236.0682   $236.07   $236.05   $236.10  
  Purchase #3 $115.76   7.649%   $124.6145   $124.61   $124.60   $124.60  
  Purchase #4 $37.31   9.650%   $40.9104   $40.91   $40.90   $40.90  
  Purchase #5 $175.88   10.838%   $194.9419   $194.94   $194.95   $194.90  
  Purchase #6 $215.81   13.646%   $245.2594   $245.26   $245.25   $245.30  
  Purchase #7 $158.65   3.439%   $164.106   $164.11   $164.10   $164.10  
  7 purchase totals = $968.53       $1,068.2521   $1,068.25   $1,068.20   $1,068.30