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	$11.87	11.479%	$13.2326	$13.23	$13.25	$13.20
Purchase #2	$134.59	9.262%	$147.0557	$147.06	$147.05	$147.10
Purchase #3	$62.82	4.130%	$65.4145	$65.41	$65.40	$65.40
Purchase #4	$145.87	4.521%	$152.4648	$152.46	$152.45	$152.50
Purchase #5	$223.58	5.321%	$235.4767	$235.48	$235.50	$235.50
Purchase #6	$98.79	5.320%	$104.0456	$104.05	$104.05	$104.00
Purchase #7	$147.36	3.772%	$152.9184	$152.92	$152.90	$152.90
7 purchase totals =	$824.88		$870.6083	$870.61	$870.60	$870.60