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 $59.72   4.252%   $62.2593   $62.26   $62.25   $62.30  
  Purchase #2 $154.85   12.315%   $173.9198   $173.92   $173.90   $173.90  
  Purchase #3 $208.59   11.438%   $232.4485   $232.45   $232.45   $232.40  
  Purchase #4 $61.49   12.694%   $69.2955   $69.30   $69.30   $69.30  
  Purchase #5 $70.67   7.383%   $75.8876   $75.89   $75.90   $75.90  
  Purchase #6 $23.42   9.377%   $25.6161   $25.62   $25.60   $25.60  
  Purchase #7 $14.89   7.817%   $16.054   $16.05   $16.05   $16.10  
  7 purchase totals = $593.63       $655.4808   $655.49   $655.45   $655.50