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 $49.33   8.283%   $53.416   $53.42   $53.40   $53.40  
  Purchase #2 $159.71   10.633%   $176.692   $176.69   $176.70   $176.70  
  Purchase #3 $22.38   11.125%   $24.8698   $24.87   $24.85   $24.90  
  Purchase #4 $64.25   11.560%   $71.6773   $71.68   $71.70   $71.70  
  Purchase #5 $70.93   5.718%   $74.9858   $74.99   $75.00   $75.00  
  Purchase #6 $236.37   4.672%   $247.4132   $247.41   $247.40   $247.40  
  Purchase #7 $116.97   13.569%   $132.8417   $132.84   $132.85   $132.80  
  7 purchase totals = $719.94       $781.8958   $781.90   $781.90   $781.90