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 $195.44   9.282%   $213.5807   $213.58   $213.60   $213.60  
  Purchase #2 $125.88   5.351%   $132.6158   $132.62   $132.60   $132.60  
  Purchase #3 $5.39   11.220%   $5.9948   $5.99   $6.00   $6.00  
  Purchase #4 $72.95   3.763%   $75.6951   $75.70   $75.70   $75.70  
  Purchase #5 $114.26   3.281%   $118.0089   $118.01   $118.00   $118.00  
  Purchase #6 $201.90   6.583%   $215.1911   $215.19   $215.20   $215.20  
  Purchase #7 $33.50   4.147%   $34.8892   $34.89   $34.90   $34.90  
  7 purchase totals = $749.32       $795.9756   $795.98   $796.00   $796.00