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 $199.39   13.493%   $226.2937   $226.29   $226.30   $226.30  
  Purchase #2 $208.75   10.872%   $231.4453   $231.45   $231.45   $231.40  
  Purchase #3 $64.66   13.215%   $73.2048   $73.20   $73.20   $73.20  
  Purchase #4 $244.71   3.165%   $252.4551   $252.46   $252.45   $252.50  
  Purchase #5 $171.87   9.773%   $188.6669   $188.67   $188.65   $188.70  
  Purchase #6 $83.35   9.775%   $91.4975   $91.50   $91.50   $91.50  
  Purchase #7 $79.33   12.567%   $89.2994   $89.30   $89.30   $89.30  
  7 purchase totals = $1,052.06       $1,152.8627   $1,152.87   $1,152.85   $1,152.90