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 $217.86   10.602%   $240.9575   $240.96   $240.95   $241.00  
  Purchase #2 $188.44   9.458%   $206.2627   $206.26   $206.25   $206.30  
  Purchase #3 $120.33   5.199%   $126.586   $126.59   $126.60   $126.60  
  Purchase #4 $7.50   10.400%   $8.28   $8.28   $8.30   $8.30  
  Purchase #5 $171.57   6.267%   $182.3223   $182.32   $182.30   $182.30  
  Purchase #6 $213.49   13.583%   $242.4883   $242.49   $242.50   $242.50  
  Purchase #7 $205.77   9.428%   $225.17   $225.17   $225.15   $225.20  
  7 purchase totals = $1,124.96       $1,232.0668   $1,232.07   $1,232.05   $1,232.20