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	$156.74	10.401%	$173.0425	$173.04	$173.05	$173.00
Purchase #2	$61.93	10.162%	$68.2233	$68.22	$68.20	$68.20
Purchase #3	$42.94	4.406%	$44.8319	$44.83	$44.85	$44.80
Purchase #4	$56.52	10.776%	$62.6106	$62.61	$62.60	$62.60
Purchase #5	$53.38	5.410%	$56.2679	$56.27	$56.25	$56.30
Purchase #6	$90.65	6.267%	$96.331	$96.33	$96.35	$96.30
Purchase #7	$131.59	11.386%	$146.5728	$146.57	$146.55	$146.60
7 purchase totals =	$593.75		$647.8800	$647.87	$647.85	$647.80