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	$224.39	3.126%	$231.4044	$231.40	$231.40	$231.40
Purchase #2	$207.89	7.178%	$222.8123	$222.81	$222.80	$222.80
Purchase #3	$99.51	9.647%	$109.1097	$109.11	$109.10	$109.10
Purchase #4	$74.54	13.518%	$84.6163	$84.62	$84.60	$84.60
Purchase #5	$65.69	8.234%	$71.0989	$71.10	$71.10	$71.10
Purchase #6	$139.93	13.444%	$158.7422	$158.74	$158.75	$158.70
Purchase #7	$76.25	8.748%	$82.9204	$82.92	$82.90	$82.90
7 purchase totals =	$888.20		$960.7042	$960.70	$960.65	$960.60