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	$47.43	13.556%	$53.8596	$53.86	$53.85	$53.90
Purchase #2	$123.61	5.269%	$130.123	$130.12	$130.10	$130.10
Purchase #3	$46.27	8.222%	$50.0743	$50.07	$50.05	$50.10
Purchase #4	$34.31	12.366%	$38.5528	$38.55	$38.55	$38.60
Purchase #5	$106.42	3.138%	$109.7595	$109.76	$109.75	$109.80
Purchase #6	$119.64	12.119%	$134.1392	$134.14	$134.15	$134.10
Purchase #7	$114.51	4.843%	$120.0557	$120.06	$120.05	$120.10
7 purchase totals =	$592.19		$636.5641	$636.56	$636.50	$636.70