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	$18.85	8.179%	$20.3917	$20.39	$20.40	$20.40
Purchase #2	$145.55	4.684%	$152.3676	$152.37	$152.35	$152.40
Purchase #3	$108.36	3.445%	$112.093	$112.09	$112.10	$112.10
Purchase #4	$17.39	12.154%	$19.5036	$19.50	$19.50	$19.50
Purchase #5	$246.66	10.114%	$271.6072	$271.61	$271.60	$271.60
Purchase #6	$115.61	13.867%	$131.6416	$131.64	$131.65	$131.60
Purchase #7	$102.56	13.346%	$116.2477	$116.25	$116.25	$116.20
7 purchase totals =	$754.98		$823.8524	$823.85	$823.85	$823.80