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	$18.27	11.201%	$20.3164	$20.32	$20.30	$20.30
Purchase #2	$233.52	4.673%	$244.4324	$244.43	$244.45	$244.40
Purchase #3	$225.85	6.646%	$240.86	$240.86	$240.85	$240.90
Purchase #4	$111.87	5.539%	$118.0665	$118.07	$118.05	$118.10
Purchase #5	$159.94	8.840%	$174.0787	$174.08	$174.10	$174.10
Purchase #6	$127.46	7.398%	$136.8895	$136.89	$136.90	$136.90
Purchase #7	$223.29	11.435%	$248.8232	$248.82	$248.80	$248.80
7 purchase totals =	$1,100.20		$1,183.4667	$1,183.47	$1,183.45	$1,183.50