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	$60.55	4.793%	$63.4522	$63.45	$63.45	$63.50
Purchase #2	$222.76	12.253%	$250.0548	$250.05	$250.05	$250.10
Purchase #3	$20.89	4.573%	$21.8453	$21.85	$21.85	$21.80
Purchase #4	$214.66	7.104%	$229.9094	$229.91	$229.90	$229.90
Purchase #5	$132.86	10.534%	$146.8555	$146.86	$146.85	$146.90
Purchase #6	$61.68	10.792%	$68.3365	$68.34	$68.35	$68.30
Purchase #7	$180.61	11.163%	$200.7715	$200.77	$200.75	$200.80
7 purchase totals =	$894.01		$981.2252	$981.23	$981.20	$981.30