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	$20.61	7.523%	$22.1605	$22.16	$22.15	$22.20
Purchase #2	$231.28	3.283%	$238.8729	$238.87	$238.85	$238.90
Purchase #3	$42.56	9.168%	$46.4619	$46.46	$46.45	$46.50
Purchase #4	$91.47	9.290%	$99.9676	$99.97	$99.95	$100.00
Purchase #5	$242.65	9.864%	$266.585	$266.59	$266.60	$266.60
Purchase #6	$73.95	6.347%	$78.6436	$78.64	$78.65	$78.60
Purchase #7	$28.62	10.859%	$31.7278	$31.73	$31.75	$31.70
7 purchase totals =	$731.14		$784.4193	$784.42	$784.40	$784.50