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	$50.55	6.650%	$53.9116	$53.91	$53.90	$53.90
Purchase #2	$208.40	4.187%	$217.1257	$217.13	$217.15	$217.10
Purchase #3	$109.25	6.116%	$115.9317	$115.93	$115.95	$115.90
Purchase #4	$50.32	8.405%	$54.5494	$54.55	$54.55	$54.50
Purchase #5	$235.46	6.242%	$250.1574	$250.16	$250.15	$250.20
Purchase #6	$155.27	9.133%	$169.4508	$169.45	$169.45	$169.50
Purchase #7	$85.94	4.771%	$90.0402	$90.04	$90.05	$90.00
7 purchase totals =	$895.19		$951.1668	$951.17	$951.20	$951.10