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 $94.39   4.327%   $98.4743   $98.47   $98.45   $98.50  
  Purchase #2 $118.82   4.325%   $123.959   $123.96   $123.95   $124.00  
  Purchase #3 $146.66   5.583%   $154.848   $154.85   $154.85   $154.80  
  Purchase #4 $136.27   5.134%   $143.2661   $143.27   $143.25   $143.30  
  Purchase #5 $130.50   7.262%   $139.9769   $139.98   $140.00   $140.00  
  Purchase #6 $91.50   5.749%   $96.7603   $96.76   $96.75   $96.80  
  Purchase #7 $82.90   6.322%   $88.1409   $88.14   $88.15   $88.10  
  7 purchase totals = $801.04       $845.4255   $845.43   $845.40   $845.50