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 $220.71   4.627%   $230.9223   $230.92   $230.90   $230.90  
  Purchase #2 $220.65   10.247%   $243.26   $243.26   $243.25   $243.30  
  Purchase #3 $222.85   10.286%   $245.7724   $245.77   $245.75   $245.80  
  Purchase #4 $158.79   12.204%   $178.1687   $178.17   $178.15   $178.20  
  Purchase #5 $98.85   7.338%   $106.1036   $106.10   $106.10   $106.10  
  Purchase #6 $66.58   8.869%   $72.485   $72.49   $72.50   $72.50  
  Purchase #7 $164.94   5.575%   $174.1354   $174.14   $174.15   $174.10  
  7 purchase totals = $1,153.37       $1,250.8474   $1,250.85   $1,250.80   $1,250.90