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 $220.91   9.347%   $241.5585   $241.56   $241.55   $241.60  
  Purchase #2 $46.37   5.164%   $48.7645   $48.76   $48.75   $48.80  
  Purchase #3 $151.39   9.153%   $165.2467   $165.25   $165.25   $165.20  
  Purchase #4 $89.30   3.861%   $92.7479   $92.75   $92.75   $92.70  
  Purchase #5 $158.79   9.721%   $174.226   $174.23   $174.25   $174.20  
  Purchase #6 $29.91   12.659%   $33.6963   $33.70   $33.70   $33.70  
  Purchase #7 $89.67   13.165%   $101.4751   $101.48   $101.50   $101.50  
  7 purchase totals = $786.34       $857.7150   $857.73   $857.75   $857.70