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 $223.56   4.589%   $233.8192   $233.82   $233.80   $233.80  
  Purchase #2 $70.61   8.232%   $76.4226   $76.42   $76.40   $76.40  
  Purchase #3 $210.44   10.681%   $232.9171   $232.92   $232.90   $232.90  
  Purchase #4 $190.50   7.422%   $204.6389   $204.64   $204.65   $204.60  
  Purchase #5 $120.92   3.590%   $125.261   $125.26   $125.25   $125.30  
  Purchase #6 $225.81   9.844%   $248.0387   $248.04   $248.05   $248.00  
  Purchase #7 $234.99   3.842%   $244.0183   $244.02   $244.00   $244.00  
  7 purchase totals = $1,276.83       $1,365.1158   $1,365.12   $1,365.05   $1,365.00