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 $216.46   4.382%   $225.9453   $225.95   $225.95   $225.90  
  Purchase #2 $176.96   3.203%   $182.628   $182.63   $182.65   $182.60  
  Purchase #3 $57.50   5.394%   $60.6016   $60.60   $60.60   $60.60  
  Purchase #4 $113.36   4.147%   $118.061   $118.06   $118.05   $118.10  
  Purchase #5 $108.54   13.240%   $122.9107   $122.91   $122.90   $122.90  
  Purchase #6 $120.65   7.743%   $129.9919   $129.99   $130.00   $130.00  
  Purchase #7 $117.51   13.697%   $133.6053   $133.61   $133.60   $133.60  
  7 purchase totals = $910.98       $973.7438   $973.75   $973.75   $973.70