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	$216.60	3.289%	$223.724	$223.72	$223.70	$223.70
Purchase #2	$171.41	11.668%	$191.4101	$191.41	$191.40	$191.40
Purchase #3	$211.78	7.168%	$226.9604	$226.96	$226.95	$227.00
Purchase #4	$105.52	5.827%	$111.6687	$111.67	$111.65	$111.70
Purchase #5	$222.92	12.446%	$250.6646	$250.66	$250.65	$250.70
Purchase #6	$28.68	8.639%	$31.1577	$31.16	$31.15	$31.20
Purchase #7	$246.80	10.714%	$273.2422	$273.24	$273.25	$273.20
7 purchase totals =	$1,203.71		$1,308.8277	$1,308.82	$1,308.75	$1,308.90