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	$83.81	5.470%	$88.3944	$88.39	$88.40	$88.40
Purchase #2	$186.40	7.559%	$200.49	$200.49	$200.50	$200.50
Purchase #3	$11.44	8.250%	$12.3838	$12.38	$12.40	$12.40
Purchase #4	$114.35	8.628%	$124.2161	$124.22	$124.20	$124.20
Purchase #5	$78.92	12.624%	$88.8829	$88.88	$88.90	$88.90
Purchase #6	$197.78	10.493%	$218.5331	$218.53	$218.55	$218.50
Purchase #7	$161.84	6.836%	$172.9034	$172.90	$172.90	$172.90
7 purchase totals =	$834.54		$905.8037	$905.79	$905.85	$905.80