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 $134.85   12.596%   $151.8357   $151.84   $151.85   $151.80  
  Purchase #2 $168.55   8.605%   $183.0537   $183.05   $183.05   $183.10  
  Purchase #3 $231.58   13.316%   $262.4172   $262.42   $262.40   $262.40  
  Purchase #4 $111.77   10.143%   $123.1068   $123.11   $123.10   $123.10  
  Purchase #5 $235.79   3.783%   $244.7099   $244.71   $244.70   $244.70  
  Purchase #6 $179.82   3.345%   $185.835   $185.84   $185.85   $185.80  
  Purchase #7 $190.63   9.370%   $208.492   $208.49   $208.50   $208.50  
  7 purchase totals = $1,252.99       $1,359.4503   $1,359.46   $1,359.45   $1,359.40