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	$121.45	4.667%	$127.1181	$127.12	$127.10	$127.10
Purchase #2	$191.79	3.403%	$198.3166	$198.32	$198.30	$198.30
Purchase #3	$83.63	13.572%	$94.9803	$94.98	$95.00	$95.00
Purchase #4	$216.62	12.120%	$242.8743	$242.87	$242.85	$242.90
Purchase #5	$180.65	10.403%	$199.443	$199.44	$199.45	$199.40
Purchase #6	$35.81	6.493%	$38.1351	$38.14	$38.15	$38.10
Purchase #7	$69.31	12.227%	$77.7845	$77.78	$77.80	$77.80
7 purchase totals =	$899.26		$978.6519	$978.65	$978.65	$978.60