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	$97.77	7.287%	$104.8945	$104.89	$104.90	$104.90
Purchase #2	$113.94	4.715%	$119.3123	$119.31	$119.30	$119.30
Purchase #3	$244.82	12.551%	$275.5474	$275.55	$275.55	$275.50
Purchase #4	$110.99	13.802%	$126.3088	$126.31	$126.30	$126.30
Purchase #5	$49.30	10.164%	$54.3109	$54.31	$54.30	$54.30
Purchase #6	$25.28	8.437%	$27.4129	$27.41	$27.40	$27.40
Purchase #7	$9.96	4.355%	$10.3938	$10.39	$10.40	$10.40
7 purchase totals =	$652.06		$718.1806	$718.17	$718.15	$718.10