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	$245.83	3.136%	$253.5392	$253.54	$253.55	$253.50
Purchase #2	$31.60	8.821%	$34.3874	$34.39	$34.40	$34.40
Purchase #3	$73.81	7.233%	$79.1487	$79.15	$79.15	$79.10
Purchase #4	$160.76	3.748%	$166.7853	$166.79	$166.80	$166.80
Purchase #5	$32.82	10.515%	$36.271	$36.27	$36.25	$36.30
Purchase #6	$134.78	8.717%	$146.5288	$146.53	$146.55	$146.50
Purchase #7	$99.66	4.172%	$103.8178	$103.82	$103.80	$103.80
7 purchase totals =	$779.26		$820.4782	$820.49	$820.50	$820.40