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	$87.35	4.638%	$91.4013	$91.40	$91.40	$91.40
Purchase #2	$138.74	10.185%	$152.8707	$152.87	$152.85	$152.90
Purchase #3	$48.37	11.786%	$54.0709	$54.07	$54.05	$54.10
Purchase #4	$60.45	11.444%	$67.3679	$67.37	$67.35	$67.40
Purchase #5	$37.61	13.753%	$42.7825	$42.78	$42.80	$42.80
Purchase #6	$148.61	9.820%	$163.2035	$163.20	$163.20	$163.20
Purchase #7	$33.50	10.625%	$37.0594	$37.06	$37.05	$37.10
7 purchase totals =	$554.63		$608.7562	$608.75	$608.70	$608.90