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	$166.95	10.399%	$184.3111	$184.31	$184.30	$184.30
Purchase #2	$125.58	4.683%	$131.4609	$131.46	$131.45	$131.50
Purchase #3	$83.68	6.139%	$88.8171	$88.82	$88.80	$88.80
Purchase #4	$7.48	3.720%	$7.7583	$7.76	$7.75	$7.80
Purchase #5	$154.56	8.784%	$168.1366	$168.14	$168.15	$168.10
Purchase #6	$50.43	10.841%	$55.8971	$55.90	$55.90	$55.90
Purchase #7	$221.46	5.700%	$234.0832	$234.08	$234.10	$234.10
7 purchase totals =	$810.14		$870.4643	$870.47	$870.45	$870.50