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	$209.82	13.451%	$238.0429	$238.04	$238.05	$238.00
Purchase #2	$100.60	4.755%	$105.3835	$105.38	$105.40	$105.40
Purchase #3	$35.91	4.138%	$37.396	$37.40	$37.40	$37.40
Purchase #4	$126.78	5.816%	$134.1535	$134.15	$134.15	$134.20
Purchase #5	$45.90	13.294%	$52.0019	$52.00	$52.00	$52.00
Purchase #6	$149.35	11.137%	$165.9831	$165.98	$166.00	$166.00
Purchase #7	$231.96	3.778%	$240.7234	$240.72	$240.70	$240.70
7 purchase totals =	$900.32		$973.6843	$973.67	$973.70	$973.70