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 $191.43   9.153%   $208.9516   $208.95   $208.95   $209.00  
  Purchase #2 $221.26   8.303%   $239.6312   $239.63   $239.65   $239.60  
  Purchase #3 $227.96   8.730%   $247.8609   $247.86   $247.85   $247.90  
  Purchase #4 $223.90   8.450%   $242.8196   $242.82   $242.80   $242.80  
  Purchase #5 $139.49   12.248%   $156.5747   $156.57   $156.55   $156.60  
  Purchase #6 $132.89   5.444%   $140.1245   $140.12   $140.10   $140.10  
  Purchase #7 $248.94   7.781%   $268.31   $268.31   $268.30   $268.30  
  7 purchase totals = $1,385.87       $1,504.2725   $1,504.26   $1,504.20   $1,504.30