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 $93.37   4.460%   $97.5343   $97.53   $97.55   $97.50  
  Purchase #2 $171.79   4.504%   $179.5274   $179.53   $179.55   $179.50  
  Purchase #3 $75.34   12.660%   $84.878   $84.88   $84.90   $84.90  
  Purchase #4 $149.30   8.472%   $161.9487   $161.95   $161.95   $161.90  
  Purchase #5 $47.96   6.644%   $51.1465   $51.15   $51.15   $51.10  
  Purchase #6 $195.72   9.493%   $214.2997   $214.30   $214.30   $214.30  
  Purchase #7 $12.53   7.744%   $13.5003   $13.50   $13.50   $13.50  
  7 purchase totals = $746.01       $802.8349   $802.84   $802.90   $802.70