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 $206.37   10.157%   $227.331   $227.33   $227.35   $227.30  
  Purchase #2 $57.40   9.210%   $62.6865   $62.69   $62.70   $62.70  
  Purchase #3 $74.61   3.703%   $77.3728   $77.37   $77.35   $77.40  
  Purchase #4 $244.56   3.566%   $253.281   $253.28   $253.30   $253.30  
  Purchase #5 $144.54   8.836%   $157.3116   $157.31   $157.30   $157.30  
  Purchase #6 $152.50   3.175%   $157.3419   $157.34   $157.35   $157.30  
  Purchase #7 $219.26   7.519%   $235.7462   $235.75   $235.75   $235.70  
  7 purchase totals = $1,099.24       $1,171.0710   $1,171.07   $1,171.10   $1,171.00