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	$24.40	13.773%	$27.7606	$27.76	$27.75	$27.80
Purchase #2	$100.52	10.580%	$111.155	$111.16	$111.15	$111.20
Purchase #3	$165.92	5.354%	$174.8034	$174.80	$174.80	$174.80
Purchase #4	$158.66	5.696%	$167.6973	$167.70	$167.70	$167.70
Purchase #5	$128.30	4.653%	$134.2698	$134.27	$134.25	$134.30
Purchase #6	$133.29	9.573%	$146.0499	$146.05	$146.05	$146.00
Purchase #7	$123.76	6.148%	$131.3688	$131.37	$131.35	$131.40
7 purchase totals =	$834.85		$893.1048	$893.11	$893.05	$893.20