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 $113.37   11.351%   $126.2386   $126.24   $126.25   $126.20  
  Purchase #2 $106.90   8.793%   $116.2997   $116.30   $116.30   $116.30  
  Purchase #3 $166.92   4.566%   $174.5416   $174.54   $174.55   $174.50  
  Purchase #4 $125.93   11.541%   $140.4636   $140.46   $140.45   $140.50  
  Purchase #5 $48.73   12.346%   $54.7462   $54.75   $54.75   $54.70  
  Purchase #6 $6.32   6.199%   $6.7118   $6.71   $6.70   $6.70  
  Purchase #7 $86.61   12.215%   $97.1894   $97.19   $97.20   $97.20  
  7 purchase totals = $654.78       $716.1909   $716.19   $716.20   $716.10