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 $208.86   8.573%   $226.7656   $226.77   $226.75   $226.80  
  Purchase #2 $10.29   10.238%   $11.3435   $11.34   $11.35   $11.30  
  Purchase #3 $204.62   11.795%   $228.7549   $228.75   $228.75   $228.80  
  Purchase #4 $185.35   10.180%   $204.2186   $204.22   $204.20   $204.20  
  Purchase #5 $250.91   4.555%   $262.339   $262.34   $262.35   $262.30  
  Purchase #6 $105.34   5.209%   $110.8272   $110.83   $110.85   $110.80  
  Purchase #7 $160.86   13.151%   $182.0147   $182.01   $182.00   $182.00  
  7 purchase totals = $1,126.23       $1,226.2635   $1,226.26   $1,226.25   $1,226.20