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	$116.42	11.777%	$130.1308	$130.13	$130.15	$130.10
Purchase #2	$235.77	5.185%	$247.9947	$247.99	$248.00	$248.00
Purchase #3	$94.53	9.677%	$103.6777	$103.68	$103.70	$103.70
Purchase #4	$134.89	7.162%	$144.5508	$144.55	$144.55	$144.60
Purchase #5	$73.56	6.411%	$78.2759	$78.28	$78.30	$78.30
Purchase #6	$183.92	3.367%	$190.1126	$190.11	$190.10	$190.10
Purchase #7	$131.79	3.307%	$136.1483	$136.15	$136.15	$136.10
7 purchase totals =	$970.88		$1,030.8908	$1,030.89	$1,030.95	$1,030.90