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	$154.46	11.479%	$172.1905	$172.19	$172.20	$172.20
Purchase #2	$204.33	10.658%	$226.1075	$226.11	$226.10	$226.10
Purchase #3	$248.82	9.262%	$271.8657	$271.87	$271.85	$271.90
Purchase #4	$104.40	7.153%	$111.8677	$111.87	$111.85	$111.90
Purchase #5	$152.84	4.410%	$159.5802	$159.58	$159.60	$159.60
Purchase #6	$81.88	13.173%	$92.6661	$92.67	$92.65	$92.70
Purchase #7	$110.55	11.478%	$123.2389	$123.24	$123.25	$123.20
7 purchase totals =	$1,057.28		$1,157.5166	$1,157.53	$1,157.50	$1,157.60