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 $48.64   4.302%   $50.7325   $50.73   $50.75   $50.70  
  Purchase #2 $227.47   9.298%   $248.6202   $248.62   $248.60   $248.60  
  Purchase #3 $244.73   11.658%   $273.2606   $273.26   $273.25   $273.30  
  Purchase #4 $27.92   4.804%   $29.2613   $29.26   $29.25   $29.30  
  Purchase #5 $23.64   12.532%   $26.6026   $26.60   $26.60   $26.60  
  Purchase #6 $116.78   11.583%   $130.3066   $130.31   $130.30   $130.30  
  Purchase #7 $214.43   4.464%   $224.0022   $224.00   $224.00   $224.00  
  7 purchase totals = $903.61       $982.7860   $982.78   $982.75   $982.80