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	$86.47	9.624%	$94.7919	$94.79	$94.80	$94.80
Purchase #2	$171.43	8.362%	$185.765	$185.77	$185.75	$185.80
Purchase #3	$122.56	13.232%	$138.7771	$138.78	$138.80	$138.80
Purchase #4	$98.88	3.622%	$102.4614	$102.46	$102.45	$102.50
Purchase #5	$228.90	11.430%	$255.0633	$255.06	$255.05	$255.10
Purchase #6	$244.53	12.634%	$275.4239	$275.42	$275.40	$275.40
Purchase #7	$165.65	8.144%	$179.1405	$179.14	$179.15	$179.10
7 purchase totals =	$1,118.42		$1,231.4231	$1,231.42	$1,231.40	$1,231.50