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	$237.98	13.545%	$270.2144	$270.21	$270.20	$270.20
Purchase #2	$127.90	11.656%	$142.808	$142.81	$142.80	$142.80
Purchase #3	$131.63	11.579%	$146.8714	$146.87	$146.85	$146.90
Purchase #4	$100.64	7.608%	$108.2967	$108.30	$108.30	$108.30
Purchase #5	$226.66	12.639%	$255.3076	$255.31	$255.30	$255.30
Purchase #6	$135.50	8.251%	$146.6801	$146.68	$146.70	$146.70
Purchase #7	$155.98	10.682%	$172.6418	$172.64	$172.65	$172.60
7 purchase totals =	$1,116.29		$1,242.8200	$1,242.82	$1,242.80	$1,242.80