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 $34.87   10.713%   $38.6056   $38.61   $38.60   $38.60  
  Purchase #2 $237.62   11.169%   $264.1598   $264.16   $264.15   $264.20  
  Purchase #3 $83.72   11.409%   $93.2716   $93.27   $93.25   $93.30  
  Purchase #4 $113.52   4.730%   $118.8895   $118.89   $118.90   $118.90  
  Purchase #5 $174.38   11.414%   $194.2837   $194.28   $194.30   $194.30  
  Purchase #6 $195.42   12.730%   $220.297   $220.30   $220.30   $220.30  
  Purchase #7 $28.78   13.785%   $32.7473   $32.75   $32.75   $32.70  
  7 purchase totals = $868.31       $962.2545   $962.26   $962.25   $962.30