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 $96.48   7.407%   $103.6263   $103.63   $103.65   $103.60  
  Purchase #2 $14.55   13.128%   $16.4601   $16.46   $16.45   $16.50  
  Purchase #3 $29.41   4.169%   $30.6361   $30.64   $30.65   $30.60  
  Purchase #4 $117.65   3.593%   $121.8772   $121.88   $121.90   $121.90  
  Purchase #5 $246.36   7.279%   $264.2925   $264.29   $264.30   $264.30  
  Purchase #6 $43.99   6.734%   $46.9523   $46.95   $46.95   $47.00  
  Purchase #7 $176.56   3.683%   $183.0627   $183.06   $183.05   $183.10  
  7 purchase totals = $725.00       $766.9072   $766.91   $766.95   $767.00