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 $211.55   7.473%   $227.3591   $227.36   $227.35   $227.40  
  Purchase #2 $112.42   4.344%   $117.3035   $117.30   $117.30   $117.30  
  Purchase #3 $185.90   5.855%   $196.7844   $196.78   $196.80   $196.80  
  Purchase #4 $217.49   10.821%   $241.0246   $241.02   $241.00   $241.00  
  Purchase #5 $99.26   8.685%   $107.8807   $107.88   $107.90   $107.90  
  Purchase #6 $202.69   11.457%   $225.9122   $225.91   $225.90   $225.90  
  Purchase #7 $119.63   5.721%   $126.474   $126.47   $126.45   $126.50  
  7 purchase totals = $1,148.94       $1,242.7385   $1,242.72   $1,242.70   $1,242.80