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	$85.94	12.537%	$96.7143	$96.71	$96.70	$96.70
Purchase #2	$100.50	10.240%	$110.7912	$110.79	$110.80	$110.80
Purchase #3	$37.53	7.659%	$40.4044	$40.40	$40.40	$40.40
Purchase #4	$238.72	5.201%	$251.1358	$251.14	$251.15	$251.10
Purchase #5	$163.37	5.590%	$172.5024	$172.50	$172.50	$172.50
Purchase #6	$117.83	9.361%	$128.8601	$128.86	$128.85	$128.90
Purchase #7	$98.75	12.652%	$111.2439	$111.24	$111.25	$111.20
7 purchase totals =	$842.64		$911.6521	$911.64	$911.65	$911.60