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 $198.51   9.177%   $216.7273   $216.73   $216.75   $216.70  
  Purchase #2 $51.54   11.687%   $57.5635   $57.56   $57.55   $57.60  
  Purchase #3 $27.27   5.537%   $28.7799   $28.78   $28.80   $28.80  
  Purchase #4 $184.51   6.346%   $196.219   $196.22   $196.20   $196.20  
  Purchase #5 $26.65   9.167%   $29.093   $29.09   $29.10   $29.10  
  Purchase #6 $143.41   5.855%   $151.8067   $151.81   $151.80   $151.80  
  Purchase #7 $96.97   11.645%   $108.2622   $108.26   $108.25   $108.30  
  7 purchase totals = $728.86       $788.4516   $788.45   $788.45   $788.50