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 $192.86   4.242%   $201.0411   $201.04   $201.05   $201.00  
  Purchase #2 $130.62   6.630%   $139.2801   $139.28   $139.30   $139.30  
  Purchase #3 $50.54   10.777%   $55.9867   $55.99   $56.00   $56.00  
  Purchase #4 $244.86   4.513%   $255.9105   $255.91   $255.90   $255.90  
  Purchase #5 $122.97   11.290%   $136.8533   $136.85   $136.85   $136.90  
  Purchase #6 $249.98   13.120%   $282.7774   $282.78   $282.80   $282.80  
  Purchase #7 $171.44   13.250%   $194.1558   $194.16   $194.15   $194.20  
  7 purchase totals = $1,163.27       $1,266.0049   $1,266.01   $1,266.05   $1,266.10