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	$135.85	5.645%	$143.5187	$143.52	$143.50	$143.50
Purchase #2	$11.71	7.646%	$12.6053	$12.61	$12.60	$12.60
Purchase #3	$23.77	3.446%	$24.5891	$24.59	$24.60	$24.60
Purchase #4	$158.68	7.869%	$171.1665	$171.17	$171.15	$171.20
Purchase #5	$30.26	4.158%	$31.5182	$31.52	$31.50	$31.50
Purchase #6	$22.31	11.417%	$24.8571	$24.86	$24.85	$24.90
Purchase #7	$58.63	11.857%	$65.5818	$65.58	$65.60	$65.60
7 purchase totals =	$441.21		$473.8367	$473.85	$473.80	$473.90