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 $203.53   10.174%   $224.2371   $224.24   $224.25   $224.20  
  Purchase #2 $119.78   13.759%   $136.2605   $136.26   $136.25   $136.30  
  Purchase #3 $164.58   5.264%   $173.2435   $173.24   $173.25   $173.20  
  Purchase #4 $27.67   7.494%   $29.7436   $29.74   $29.75   $29.70  
  Purchase #5 $214.74   11.502%   $239.4394   $239.44   $239.45   $239.40  
  Purchase #6 $74.49   13.213%   $84.3324   $84.33   $84.35   $84.30  
  Purchase #7 $201.26   6.339%   $214.0179   $214.02   $214.00   $214.00  
  7 purchase totals = $1,006.05       $1,101.2744   $1,101.27   $1,101.30   $1,101.10