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	$103.51	11.492%	$115.4054	$115.41	$115.40	$115.40
Purchase #2	$87.84	5.560%	$92.7239	$92.72	$92.70	$92.70
Purchase #3	$133.56	6.621%	$142.403	$142.40	$142.40	$142.40
Purchase #4	$66.98	6.468%	$71.3123	$71.31	$71.30	$71.30
Purchase #5	$136.63	5.428%	$144.0463	$144.05	$144.05	$144.00
Purchase #6	$183.90	4.240%	$191.6974	$191.70	$191.70	$191.70
Purchase #7	$47.59	12.316%	$53.4512	$53.45	$53.45	$53.50
7 purchase totals =	$760.01		$811.0395	$811.04	$811.00	$811.00