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 $88.31   5.746%   $93.3843   $93.38   $93.40   $93.40  
  Purchase #2 $53.88   8.134%   $58.2626   $58.26   $58.25   $58.30  
  Purchase #3 $170.80   3.627%   $176.9949   $176.99   $177.00   $177.00  
  Purchase #4 $104.28   5.248%   $109.7526   $109.75   $109.75   $109.80  
  Purchase #5 $126.34   10.179%   $139.2001   $139.20   $139.20   $139.20  
  Purchase #6 $61.54   6.710%   $65.6693   $65.67   $65.65   $65.70  
  Purchase #7 $77.74   7.598%   $83.6467   $83.65   $83.65   $83.60  
  7 purchase totals = $682.89       $726.9105   $726.90   $726.90   $727.00