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	$69.68	12.585%	$78.4492	$78.45	$78.45	$78.40
Purchase #2	$209.68	10.560%	$231.8222	$231.82	$231.80	$231.80
Purchase #3	$231.72	13.275%	$262.4808	$262.48	$262.50	$262.50
Purchase #4	$48.76	6.371%	$51.8665	$51.87	$51.85	$51.90
Purchase #5	$89.78	8.792%	$97.6735	$97.67	$97.65	$97.70
Purchase #6	$175.47	7.513%	$188.6531	$188.65	$188.65	$188.70
Purchase #7	$69.42	3.162%	$71.6151	$71.62	$71.60	$71.60
7 purchase totals =	$894.51		$982.5604	$982.56	$982.50	$982.60