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 $224.96   12.262%   $252.5446   $252.54   $252.55   $252.50  
  Purchase #2 $119.42   3.334%   $123.4015   $123.40   $123.40   $123.40  
  Purchase #3 $183.47   6.162%   $194.7754   $194.78   $194.80   $194.80  
  Purchase #4 $245.59   3.396%   $253.9302   $253.93   $253.95   $253.90  
  Purchase #5 $119.80   12.117%   $134.3162   $134.32   $134.30   $134.30  
  Purchase #6 $243.25   13.741%   $276.675   $276.68   $276.70   $276.70  
  Purchase #7 $149.57   11.149%   $166.2456   $166.25   $166.25   $166.20  
  7 purchase totals = $1,286.06       $1,401.8885   $1,401.90   $1,401.95   $1,401.80