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 $93.63   4.390%   $97.7404   $97.74   $97.75   $97.70  
  Purchase #2 $87.26   4.242%   $90.9616   $90.96   $90.95   $91.00  
  Purchase #3 $111.85   3.703%   $115.9918   $115.99   $116.00   $116.00  
  Purchase #4 $117.25   13.660%   $133.2664   $133.27   $133.25   $133.30  
  Purchase #5 $213.26   10.596%   $235.857   $235.86   $235.85   $235.90  
  Purchase #6 $179.83   9.779%   $197.4156   $197.42   $197.40   $197.40  
  Purchase #7 $13.76   4.452%   $14.3726   $14.37   $14.35   $14.40  
  7 purchase totals = $816.84       $885.6054   $885.61   $885.55   $885.70