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 $83.62   9.157%   $91.2771   $91.28   $91.30   $91.30  
  Purchase #2 $172.83   12.117%   $193.7718   $193.77   $193.75   $193.80  
  Purchase #3 $195.39   10.181%   $215.2827   $215.28   $215.30   $215.30  
  Purchase #4 $156.49   13.481%   $177.5864   $177.59   $177.60   $177.60  
  Purchase #5 $76.93   3.649%   $79.7372   $79.74   $79.75   $79.70  
  Purchase #6 $19.67   13.150%   $22.2566   $22.26   $22.25   $22.30  
  Purchase #7 $167.47   9.287%   $183.0229   $183.02   $183.00   $183.00  
  7 purchase totals = $872.40       $962.9347   $962.94   $962.95   $963.00