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 $126.35   11.870%   $141.3477   $141.35   $141.35   $141.30  
  Purchase #2 $139.34   13.829%   $158.6093   $158.61   $158.60   $158.60  
  Purchase #3 $204.54   4.848%   $214.4561   $214.46   $214.45   $214.50  
  Purchase #4 $73.98   4.815%   $77.5421   $77.54   $77.55   $77.50  
  Purchase #5 $142.41   4.774%   $149.2087   $149.21   $149.20   $149.20  
  Purchase #6 $39.61   3.285%   $40.9112   $40.91   $40.90   $40.90  
  Purchase #7 $11.78   3.457%   $12.1872   $12.19   $12.20   $12.20  
  7 purchase totals = $738.01       $794.2623   $794.27   $794.25   $794.20