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	$38.79	10.399%	$42.8238	$42.82	$42.80	$42.80
Purchase #2	$209.51	6.483%	$223.0925	$223.09	$223.10	$223.10
Purchase #3	$46.64	7.812%	$50.2835	$50.28	$50.30	$50.30
Purchase #4	$95.81	10.346%	$105.7225	$105.72	$105.70	$105.70
Purchase #5	$171.45	9.662%	$188.0155	$188.02	$188.00	$188.00
Purchase #6	$118.93	6.338%	$126.4678	$126.47	$126.45	$126.50
Purchase #7	$7.42	5.155%	$7.8025	$7.80	$7.80	$7.80
7 purchase totals =	$688.55		$744.2081	$744.20	$744.15	$744.20