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 $188.83   12.369%   $212.1864   $212.19   $212.20   $212.20  
  Purchase #2 $77.81   6.616%   $82.9579   $82.96   $82.95   $83.00  
  Purchase #3 $45.80   7.303%   $49.1448   $49.14   $49.15   $49.10  
  Purchase #4 $56.60   8.457%   $61.3867   $61.39   $61.40   $61.40  
  Purchase #5 $217.90   11.853%   $243.7277   $243.73   $243.75   $243.70  
  Purchase #6 $59.66   4.554%   $62.3769   $62.38   $62.40   $62.40  
  Purchase #7 $39.44   3.826%   $40.949   $40.95   $40.95   $40.90  
  7 purchase totals = $686.04       $752.7294   $752.74   $752.80   $752.70