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	$64.63	10.853%	$71.6443	$71.64	$71.65	$71.60
Purchase #2	$12.35	4.269%	$12.8772	$12.88	$12.90	$12.90
Purchase #3	$83.42	6.120%	$88.5253	$88.53	$88.55	$88.50
Purchase #4	$164.52	11.508%	$183.453	$183.45	$183.45	$183.50
Purchase #5	$7.42	6.357%	$7.8917	$7.89	$7.90	$7.90
Purchase #6	$184.67	8.476%	$200.3226	$200.32	$200.30	$200.30
Purchase #7	$64.95	9.563%	$71.1612	$71.16	$71.15	$71.20
7 purchase totals =	$581.96		$635.8753	$635.87	$635.90	$635.90