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 $112.91   4.119%   $117.5608   $117.56   $117.55   $117.60  
  Purchase #2 $23.63   11.130%   $26.26   $26.26   $26.25   $26.30  
  Purchase #3 $70.95   7.429%   $76.2209   $76.22   $76.20   $76.20  
  Purchase #4 $118.74   5.339%   $125.0795   $125.08   $125.10   $125.10  
  Purchase #5 $204.49   11.172%   $227.3356   $227.34   $227.35   $227.30  
  Purchase #6 $106.99   9.335%   $116.9775   $116.98   $117.00   $117.00  
  Purchase #7 $87.73   9.548%   $96.1065   $96.11   $96.10   $96.10  
  7 purchase totals = $725.44       $785.5408   $785.55   $785.55   $785.60