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 $68.45   11.306%   $76.189   $76.19   $76.20   $76.20  
  Purchase #2 $112.53   6.827%   $120.2124   $120.21   $120.20   $120.20  
  Purchase #3 $132.36   8.755%   $143.9481   $143.95   $143.95   $143.90  
  Purchase #4 $131.87   3.159%   $136.0358   $136.04   $136.05   $136.00  
  Purchase #5 $116.83   5.282%   $123.001   $123.00   $123.00   $123.00  
  Purchase #6 $153.31   9.507%   $167.8852   $167.89   $167.90   $167.90  
  Purchase #7 $14.28   10.106%   $15.7231   $15.72   $15.70   $15.70  
  7 purchase totals = $729.63       $782.9946   $783.00   $783.00   $782.90