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	$50.71	9.594%	$55.5751	$55.58	$55.60	$55.60
Purchase #2	$48.99	12.128%	$54.9315	$54.93	$54.95	$54.90
Purchase #3	$7.31	13.631%	$8.3064	$8.31	$8.30	$8.30
Purchase #4	$94.31	6.829%	$100.7504	$100.75	$100.75	$100.80
Purchase #5	$74.25	11.312%	$82.6492	$82.65	$82.65	$82.60
Purchase #6	$151.56	10.640%	$167.686	$167.69	$167.70	$167.70
Purchase #7	$240.93	9.207%	$263.1124	$263.11	$263.10	$263.10
7 purchase totals =	$668.06		$733.0110	$733.02	$733.05	$733.00