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 $56.87   10.351%   $62.7566   $62.76   $62.75   $62.80  
  Purchase #2 $193.26   3.440%   $199.9081   $199.91   $199.90   $199.90  
  Purchase #3 $245.82   4.103%   $255.906   $255.91   $255.90   $255.90  
  Purchase #4 $126.90   13.772%   $144.3767   $144.38   $144.40   $144.40  
  Purchase #5 $72.50   4.382%   $75.677   $75.68   $75.70   $75.70  
  Purchase #6 $80.38   5.149%   $84.5188   $84.52   $84.50   $84.50  
  Purchase #7 $165.62   5.755%   $175.1514   $175.15   $175.15   $175.20  
  7 purchase totals = $941.35       $998.2946   $998.31   $998.30   $998.40