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 $153.68   13.201%   $173.9673   $173.97   $173.95   $174.00  
  Purchase #2 $174.95   10.737%   $193.7344   $193.73   $193.75   $193.70  
  Purchase #3 $45.26   3.321%   $46.7631   $46.76   $46.75   $46.80  
  Purchase #4 $154.58   3.122%   $159.406   $159.41   $159.40   $159.40  
  Purchase #5 $105.69   11.537%   $117.8835   $117.88   $117.90   $117.90  
  Purchase #6 $8.25   9.280%   $9.0156   $9.02   $9.00   $9.00  
  Purchase #7 $138.40   10.847%   $153.4122   $153.41   $153.40   $153.40  
  7 purchase totals = $780.81       $854.1821   $854.18   $854.15   $854.20