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 $59.55   13.156%   $67.3844   $67.38   $67.40   $67.40  
  Purchase #2 $166.93   11.545%   $186.2021   $186.20   $186.20   $186.20  
  Purchase #3 $200.37   8.164%   $216.7282   $216.73   $216.75   $216.70  
  Purchase #4 $162.48   8.115%   $175.6653   $175.67   $175.65   $175.70  
  Purchase #5 $142.29   10.598%   $157.3699   $157.37   $157.35   $157.40  
  Purchase #6 $205.44   9.732%   $225.4334   $225.43   $225.45   $225.40  
  Purchase #7 $182.27   6.366%   $193.8733   $193.87   $193.85   $193.90  
  7 purchase totals = $1,119.33       $1,222.6566   $1,222.65   $1,222.65   $1,222.70