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	$82.34	9.153%	$89.8766	$89.88	$89.90	$89.90
Purchase #2	$238.96	12.346%	$268.462	$268.46	$268.45	$268.50
Purchase #3	$121.73	4.773%	$127.5402	$127.54	$127.55	$127.50
Purchase #4	$48.79	7.149%	$52.278	$52.28	$52.30	$52.30
Purchase #5	$214.45	3.513%	$221.9836	$221.98	$222.00	$222.00
Purchase #6	$211.41	11.233%	$235.1577	$235.16	$235.15	$235.20
Purchase #7	$244.82	4.777%	$256.5151	$256.52	$256.50	$256.50
7 purchase totals =	$1,162.50		$1,251.8132	$1,251.82	$1,251.85	$1,251.90