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 $103.52   12.664%   $116.6298   $116.63   $116.65   $116.60  
  Purchase #2 $239.39   4.174%   $249.3821   $249.38   $249.40   $249.40  
  Purchase #3 $216.76   12.647%   $244.1736   $244.17   $244.15   $244.20  
  Purchase #4 $193.26   10.398%   $213.3552   $213.36   $213.35   $213.40  
  Purchase #5 $8.65   4.199%   $9.0132   $9.01   $9.00   $9.00  
  Purchase #6 $206.49   4.573%   $215.9328   $215.93   $215.95   $215.90  
  Purchase #7 $101.74   13.406%   $115.3793   $115.38   $115.40   $115.40  
  7 purchase totals = $1,069.81       $1,163.8660   $1,163.86   $1,163.90   $1,163.90