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 $186.55   3.439%   $192.9655   $192.97   $192.95   $193.00  
  Purchase #2 $19.96   13.452%   $22.645   $22.65   $22.65   $22.60  
  Purchase #3 $166.74   9.158%   $182.01   $182.01   $182.00   $182.00  
  Purchase #4 $95.48   11.810%   $106.7562   $106.76   $106.75   $106.80  
  Purchase #5 $221.54   5.108%   $232.8563   $232.86   $232.85   $232.90  
  Purchase #6 $119.55   5.384%   $125.9866   $125.99   $126.00   $126.00  
  Purchase #7 $92.32   10.143%   $101.684   $101.68   $101.70   $101.70  
  7 purchase totals = $902.14       $964.9036   $964.92   $964.90   $965.00