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	$234.74	12.492%	$264.0637	$264.06	$264.05	$264.10
Purchase #2	$182.82	12.768%	$206.1625	$206.16	$206.15	$206.20
Purchase #3	$19.58	4.707%	$20.5016	$20.50	$20.50	$20.50
Purchase #4	$65.63	8.868%	$71.4501	$71.45	$71.45	$71.50
Purchase #5	$149.82	5.254%	$157.6915	$157.69	$157.70	$157.70
Purchase #6	$76.27	3.238%	$78.7396	$78.74	$78.75	$78.70
Purchase #7	$120.96	5.434%	$127.533	$127.53	$127.55	$127.50
7 purchase totals =	$849.82		$926.1420	$926.13	$926.15	$926.20