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	$127.79	8.435%	$138.5691	$138.57	$138.55	$138.60
Purchase #2	$150.38	9.519%	$164.6947	$164.69	$164.70	$164.70
Purchase #3	$128.27	12.583%	$144.4102	$144.41	$144.40	$144.40
Purchase #4	$164.40	12.585%	$185.0897	$185.09	$185.10	$185.10
Purchase #5	$33.72	10.486%	$37.2559	$37.26	$37.25	$37.30
Purchase #6	$99.70	6.753%	$106.4327	$106.43	$106.45	$106.40
Purchase #7	$37.42	3.251%	$38.6365	$38.64	$38.65	$38.60
7 purchase totals =	$741.68		$815.0888	$815.09	$815.10	$815.10