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	$73.89	6.323%	$78.5621	$78.56	$78.55	$78.60
Purchase #2	$88.82	8.268%	$96.1636	$96.16	$96.15	$96.20
Purchase #3	$230.42	3.771%	$239.1091	$239.11	$239.10	$239.10
Purchase #4	$130.47	13.660%	$148.2922	$148.29	$148.30	$148.30
Purchase #5	$91.75	13.500%	$104.1363	$104.14	$104.15	$104.10
Purchase #6	$202.65	10.717%	$224.368	$224.37	$224.35	$224.40
Purchase #7	$126.60	13.207%	$143.3201	$143.32	$143.30	$143.30
7 purchase totals =	$944.60		$1,033.9514	$1,033.95	$1,033.90	$1,034.00