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	$13.85	10.461%	$15.2988	$15.30	$15.30	$15.30
Purchase #2	$62.49	11.825%	$69.8794	$69.88	$69.90	$69.90
Purchase #3	$222.42	10.622%	$246.0455	$246.05	$246.05	$246.00
Purchase #4	$222.84	4.587%	$233.0617	$233.06	$233.05	$233.10
Purchase #5	$37.76	12.797%	$42.5921	$42.59	$42.60	$42.60
Purchase #6	$216.80	4.861%	$227.3386	$227.34	$227.35	$227.30
Purchase #7	$37.74	7.446%	$40.5501	$40.55	$40.55	$40.60
7 purchase totals =	$813.90		$874.7662	$874.77	$874.80	$874.80