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	$145.39	8.529%	$157.7903	$157.79	$157.80	$157.80
Purchase #2	$99.78	11.798%	$111.552	$111.55	$111.55	$111.60
Purchase #3	$35.73	9.498%	$39.1236	$39.12	$39.10	$39.10
Purchase #4	$130.63	5.340%	$137.6056	$137.61	$137.60	$137.60
Purchase #5	$215.68	4.553%	$225.4999	$225.50	$225.50	$225.50
Purchase #6	$159.72	3.370%	$165.1026	$165.10	$165.10	$165.10
Purchase #7	$151.53	13.276%	$171.6471	$171.65	$171.65	$171.60
7 purchase totals =	$938.46		$1,008.3211	$1,008.32	$1,008.30	$1,008.30