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 $24.73   4.804%   $25.918   $25.92   $25.90   $25.90  
  Purchase #2 $44.26   3.386%   $45.7586   $45.76   $45.75   $45.80  
  Purchase #3 $117.88   11.126%   $130.9953   $131.00   $131.00   $131.00  
  Purchase #4 $130.87   9.731%   $143.605   $143.61   $143.60   $143.60  
  Purchase #5 $43.59   12.805%   $49.1717   $49.17   $49.15   $49.20  
  Purchase #6 $86.34   12.412%   $97.0565   $97.06   $97.05   $97.10  
  Purchase #7 $211.34   4.583%   $221.0257   $221.03   $221.05   $221.00  
  7 purchase totals = $659.01       $713.5308   $713.55   $713.50   $713.60