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 $236.35   5.214%   $248.6733   $248.67   $248.65   $248.70  
  Purchase #2 $243.87   12.286%   $273.8319   $273.83   $273.85   $273.80  
  Purchase #3 $231.36   7.857%   $249.538   $249.54   $249.55   $249.50  
  Purchase #4 $32.72   11.373%   $36.4412   $36.44   $36.45   $36.40  
  Purchase #5 $117.71   7.298%   $126.3005   $126.30   $126.30   $126.30  
  Purchase #6 $179.33   6.434%   $190.8681   $190.87   $190.85   $190.90  
  Purchase #7 $221.66   8.495%   $240.49   $240.49   $240.50   $240.50  
  7 purchase totals = $1,263.00       $1,366.1430   $1,366.14   $1,366.15   $1,366.10