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 $208.54   6.736%   $222.5873   $222.59   $222.60   $222.60  
  Purchase #2 $222.50   13.796%   $253.1961   $253.20   $253.20   $253.20  
  Purchase #3 $112.59   10.397%   $124.296   $124.30   $124.30   $124.30  
  Purchase #4 $87.93   5.116%   $92.4285   $92.43   $92.45   $92.40  
  Purchase #5 $236.94   5.416%   $249.7727   $249.77   $249.75   $249.80  
  Purchase #6 $22.68   8.765%   $24.6679   $24.67   $24.65   $24.70  
  Purchase #7 $112.54   11.607%   $125.6025   $125.60   $125.60   $125.60  
  7 purchase totals = $1,003.72       $1,092.5510   $1,092.56   $1,092.55   $1,092.60