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	$157.71	6.815%	$168.4579	$168.46	$168.45	$168.50
Purchase #2	$123.42	4.609%	$129.1084	$129.11	$129.10	$129.10
Purchase #3	$112.82	13.303%	$127.8284	$127.83	$127.85	$127.80
Purchase #4	$25.83	4.394%	$26.965	$26.97	$26.95	$27.00
Purchase #5	$99.56	12.643%	$112.1474	$112.15	$112.15	$112.10
Purchase #6	$150.90	13.333%	$171.0195	$171.02	$171.00	$171.00
Purchase #7	$243.50	5.190%	$256.1377	$256.14	$256.15	$256.10
7 purchase totals =	$913.74		$991.6643	$991.68	$991.65	$991.60