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 $106.41   11.863%   $119.0334   $119.03   $119.05   $119.00  
  Purchase #2 $184.40   6.148%   $195.7369   $195.74   $195.75   $195.70  
  Purchase #3 $187.86   12.476%   $211.2974   $211.30   $211.30   $211.30  
  Purchase #4 $18.76   4.854%   $19.6706   $19.67   $19.65   $19.70  
  Purchase #5 $214.38   12.244%   $240.6287   $240.63   $240.65   $240.60  
  Purchase #6 $193.85   5.192%   $203.9147   $203.91   $203.90   $203.90  
  Purchase #7 $213.96   13.518%   $242.8831   $242.88   $242.90   $242.90  
  7 purchase totals = $1,119.62       $1,233.1648   $1,233.16   $1,233.20   $1,233.10