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 $38.49   12.755%   $43.3994   $43.40   $43.40   $43.40  
  Purchase #2 $101.91   5.241%   $107.2511   $107.25   $107.25   $107.30  
  Purchase #3 $62.97   3.534%   $65.1954   $65.20   $65.20   $65.20  
  Purchase #4 $76.70   4.105%   $79.8485   $79.85   $79.85   $79.80  
  Purchase #5 $83.60   5.259%   $87.9965   $88.00   $88.00   $88.00  
  Purchase #6 $125.72   12.413%   $141.3256   $141.33   $141.35   $141.30  
  Purchase #7 $244.88   13.117%   $277.0009   $277.00   $277.00   $277.00  
  7 purchase totals = $734.27       $802.0174   $802.03   $802.05   $802.00