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	$164.62	3.157%	$169.8171	$169.82	$169.80	$169.80
Purchase #2	$88.62	11.812%	$99.0878	$99.09	$99.10	$99.10
Purchase #3	$149.38	12.491%	$168.0391	$168.04	$168.05	$168.00
Purchase #4	$37.63	4.697%	$39.3975	$39.40	$39.40	$39.40
Purchase #5	$113.33	12.215%	$127.1733	$127.17	$127.15	$127.20
Purchase #6	$248.67	9.140%	$271.3984	$271.40	$271.40	$271.40
Purchase #7	$102.70	13.773%	$116.8449	$116.84	$116.85	$116.80
7 purchase totals =	$904.95		$991.7581	$991.76	$991.75	$991.70