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	$21.56	10.202%	$23.7596	$23.76	$23.75	$23.80
Purchase #2	$42.90	8.454%	$46.5268	$46.53	$46.55	$46.50
Purchase #3	$46.59	8.627%	$50.6093	$50.61	$50.60	$50.60
Purchase #4	$224.33	4.232%	$233.8236	$233.82	$233.80	$233.80
Purchase #5	$33.90	10.575%	$37.4849	$37.48	$37.50	$37.50
Purchase #6	$58.28	4.194%	$60.7243	$60.72	$60.70	$60.70
Purchase #7	$127.79	6.832%	$136.5206	$136.52	$136.50	$136.50
7 purchase totals =	$555.35		$589.4491	$589.44	$589.40	$589.40