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 $58.78   3.732%   $60.9737   $60.97   $60.95   $61.00  
  Purchase #2 $158.84   7.707%   $171.0818   $171.08   $171.10   $171.10  
  Purchase #3 $77.60   4.475%   $81.0726   $81.07   $81.05   $81.10  
  Purchase #4 $146.37   10.330%   $161.49   $161.49   $161.50   $161.50  
  Purchase #5 $33.81   5.425%   $35.6442   $35.64   $35.65   $35.60  
  Purchase #6 $227.71   4.762%   $238.5536   $238.55   $238.55   $238.60  
  Purchase #7 $68.67   8.539%   $74.5337   $74.53   $74.55   $74.50  
  7 purchase totals = $771.78       $823.3496   $823.33   $823.35   $823.40