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	$53.28	7.830%	$57.4518	$57.45	$57.45	$57.50
Purchase #2	$34.98	10.459%	$38.6386	$38.64	$38.65	$38.60
Purchase #3	$165.68	11.748%	$185.1441	$185.14	$185.15	$185.10
Purchase #4	$67.71	3.468%	$70.0582	$70.06	$70.05	$70.10
Purchase #5	$132.28	6.335%	$140.6599	$140.66	$140.65	$140.70
Purchase #6	$55.61	4.111%	$57.8961	$57.90	$57.90	$57.90
Purchase #7	$152.56	11.705%	$170.4171	$170.42	$170.40	$170.40
7 purchase totals =	$662.10		$720.2658	$720.27	$720.25	$720.30