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 $166.86   9.623%   $182.9169   $182.92   $182.90   $182.90  
  Purchase #2 $108.90   3.863%   $113.1068   $113.11   $113.10   $113.10  
  Purchase #3 $55.80   3.532%   $57.7709   $57.77   $57.75   $57.80  
  Purchase #4 $212.80   5.195%   $223.855   $223.86   $223.85   $223.90  
  Purchase #5 $231.34   4.444%   $241.6207   $241.62   $241.60   $241.60  
  Purchase #6 $199.71   12.724%   $225.1211   $225.12   $225.10   $225.10  
  Purchase #7 $201.58   7.761%   $217.2246   $217.22   $217.20   $217.20  
  7 purchase totals = $1,176.99       $1,261.6160   $1,261.62   $1,261.50   $1,261.60