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 $164.26   13.696%   $186.757   $186.76   $186.75   $186.80  
  Purchase #2 $18.43   4.350%   $19.2317   $19.23   $19.25   $19.20  
  Purchase #3 $98.81   7.452%   $106.1733   $106.17   $106.15   $106.20  
  Purchase #4 $208.53   5.225%   $219.4257   $219.43   $219.45   $219.40  
  Purchase #5 $107.28   9.510%   $117.4823   $117.48   $117.50   $117.50  
  Purchase #6 $200.33   7.204%   $214.7618   $214.76   $214.75   $214.80  
  Purchase #7 $236.59   13.282%   $268.0139   $268.01   $268.00   $268.00  
  7 purchase totals = $1,034.23       $1,131.8457   $1,131.84   $1,131.85   $1,131.90