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	$162.82	4.705%	$170.4807	$170.48	$170.50	$170.50
Purchase #2	$201.69	13.796%	$229.5152	$229.52	$229.50	$229.50
Purchase #3	$77.53	5.819%	$82.0415	$82.04	$82.05	$82.00
Purchase #4	$11.95	12.609%	$13.4568	$13.46	$13.45	$13.50
Purchase #5	$247.80	3.440%	$256.3243	$256.32	$256.30	$256.30
Purchase #6	$64.37	9.109%	$70.2335	$70.23	$70.25	$70.20
Purchase #7	$238.89	6.198%	$253.6964	$253.70	$253.70	$253.70
7 purchase totals =	$1,005.05		$1,075.7484	$1,075.75	$1,075.75	$1,075.70