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	$107.36	4.228%	$111.8992	$111.90	$111.90	$111.90
Purchase #2	$84.30	6.505%	$89.7837	$89.78	$89.80	$89.80
Purchase #3	$25.25	10.535%	$27.9101	$27.91	$27.90	$27.90
Purchase #4	$43.65	9.256%	$47.6902	$47.69	$47.70	$47.70
Purchase #5	$92.88	9.467%	$101.6729	$101.67	$101.65	$101.70
Purchase #6	$64.93	6.375%	$69.0693	$69.07	$69.05	$69.10
Purchase #7	$48.64	8.408%	$52.7297	$52.73	$52.75	$52.70
7 purchase totals =	$467.01		$500.7551	$500.75	$500.75	$500.80