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 $225.91   6.665%   $240.9669   $240.97   $240.95   $241.00  
  Purchase #2 $58.41   7.190%   $62.6097   $62.61   $62.60   $62.60  
  Purchase #3 $183.73   12.294%   $206.3178   $206.32   $206.30   $206.30  
  Purchase #4 $86.65   10.622%   $95.854   $95.85   $95.85   $95.90  
  Purchase #5 $228.51   8.635%   $248.2418   $248.24   $248.25   $248.20  
  Purchase #6 $39.46   13.581%   $44.8191   $44.82   $44.80   $44.80  
  Purchase #7 $92.61   13.130%   $104.7697   $104.77   $104.75   $104.80  
  7 purchase totals = $915.28       $1,003.5790   $1,003.58   $1,003.50   $1,003.60