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 $171.47   5.431%   $180.7825   $180.78   $180.80   $180.80  
  Purchase #2 $143.29   12.339%   $160.9706   $160.97   $160.95   $161.00  
  Purchase #3 $188.29   3.530%   $194.9366   $194.94   $194.95   $194.90  
  Purchase #4 $139.27   11.227%   $154.9058   $154.91   $154.90   $154.90  
  Purchase #5 $100.71   12.310%   $113.1074   $113.11   $113.10   $113.10  
  Purchase #6 $17.90   8.772%   $19.4702   $19.47   $19.45   $19.50  
  Purchase #7 $59.47   8.682%   $64.6332   $64.63   $64.65   $64.60  
  7 purchase totals = $820.40       $888.8063   $888.81   $888.80   $888.80