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	$44.72	11.740%	$49.9701	$49.97	$49.95	$50.00
Purchase #2	$55.60	10.457%	$61.4141	$61.41	$61.40	$61.40
Purchase #3	$60.65	7.784%	$65.371	$65.37	$65.35	$65.40
Purchase #4	$75.50	13.757%	$85.8865	$85.89	$85.90	$85.90
Purchase #5	$112.73	9.557%	$123.5036	$123.50	$123.50	$123.50
Purchase #6	$236.74	4.581%	$247.5851	$247.59	$247.60	$247.60
Purchase #7	$65.76	9.626%	$72.0901	$72.09	$72.10	$72.10
7 purchase totals =	$651.70		$705.8205	$705.82	$705.80	$705.90