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	$75.54	11.861%	$84.4998	$84.50	$84.50	$84.50
Purchase #2	$145.66	6.869%	$155.6654	$155.67	$155.65	$155.70
Purchase #3	$230.72	6.681%	$246.1344	$246.13	$246.15	$246.10
Purchase #4	$211.36	11.571%	$235.8165	$235.82	$235.80	$235.80
Purchase #5	$61.94	6.517%	$65.9766	$65.98	$66.00	$66.00
Purchase #6	$246.65	3.694%	$255.7613	$255.76	$255.75	$255.80
Purchase #7	$99.74	11.752%	$111.4614	$111.46	$111.45	$111.50
7 purchase totals =	$1,071.61		$1,155.3154	$1,155.32	$1,155.30	$1,155.40