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 $73.48   9.166%   $80.2152   $80.22   $80.20   $80.20  
  Purchase #2 $125.58   7.131%   $134.5351   $134.54   $134.55   $134.50  
  Purchase #3 $113.71   10.830%   $126.0248   $126.02   $126.00   $126.00  
  Purchase #4 $126.74   8.796%   $137.8881   $137.89   $137.90   $137.90  
  Purchase #5 $233.35   6.286%   $248.0184   $248.02   $248.00   $248.00  
  Purchase #6 $176.40   13.817%   $200.7732   $200.77   $200.75   $200.80  
  Purchase #7 $85.68   12.147%   $96.0875   $96.09   $96.10   $96.10  
  7 purchase totals = $934.94       $1,023.5423   $1,023.55   $1,023.50   $1,023.50