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 $57.73   11.103%   $64.1398   $64.14   $64.15   $64.10  
  Purchase #2 $40.69   9.457%   $44.5381   $44.54   $44.55   $44.50  
  Purchase #3 $19.25   6.832%   $20.5652   $20.57   $20.55   $20.60  
  Purchase #4 $195.71   4.783%   $205.0708   $205.07   $205.05   $205.10  
  Purchase #5 $144.90   7.674%   $156.0196   $156.02   $156.00   $156.00  
  Purchase #6 $49.77   9.321%   $54.4091   $54.41   $54.40   $54.40  
  Purchase #7 $200.31   8.653%   $217.6428   $217.64   $217.65   $217.60  
  7 purchase totals = $708.36       $762.3854   $762.39   $762.35   $762.30