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	$157.78	13.516%	$179.1055	$179.11	$179.10	$179.10
Purchase #2	$226.63	12.842%	$255.7338	$255.73	$255.75	$255.70
Purchase #3	$157.94	4.755%	$165.45	$165.45	$165.45	$165.50
Purchase #4	$106.88	12.328%	$120.0562	$120.06	$120.05	$120.10
Purchase #5	$93.82	12.206%	$105.2717	$105.27	$105.25	$105.30
Purchase #6	$233.78	11.387%	$260.4005	$260.40	$260.40	$260.40
Purchase #7	$165.60	5.766%	$175.1485	$175.15	$175.15	$175.10
7 purchase totals =	$1,142.43		$1,261.1662	$1,261.17	$1,261.15	$1,261.20