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 $127.55   6.692%   $136.0856   $136.09   $136.10   $136.10  
  Purchase #2 $220.70   11.110%   $245.2198   $245.22   $245.20   $245.20  
  Purchase #3 $195.37   11.493%   $217.8239   $217.82   $217.80   $217.80  
  Purchase #4 $175.72   12.261%   $197.265   $197.27   $197.25   $197.30  
  Purchase #5 $54.57   5.429%   $57.5326   $57.53   $57.55   $57.50  
  Purchase #6 $199.47   10.669%   $220.7515   $220.75   $220.75   $220.80  
  Purchase #7 $55.48   9.485%   $60.7423   $60.74   $60.75   $60.70  
  7 purchase totals = $1,028.86       $1,135.4207   $1,135.42   $1,135.40   $1,135.40