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 $237.58   3.132%   $245.021   $245.02   $245.00   $245.00  
  Purchase #2 $68.95   10.326%   $76.0698   $76.07   $76.05   $76.10  
  Purchase #3 $62.41   8.826%   $67.9183   $67.92   $67.90   $67.90  
  Purchase #4 $31.54   13.545%   $35.8121   $35.81   $35.80   $35.80  
  Purchase #5 $163.39   11.126%   $181.5688   $181.57   $181.55   $181.60  
  Purchase #6 $101.85   4.241%   $106.1695   $106.17   $106.15   $106.20  
  Purchase #7 $83.68   10.395%   $92.3785   $92.38   $92.40   $92.40  
  7 purchase totals = $749.40       $804.9380   $804.94   $804.85   $805.00