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	$133.63	5.563%	$141.0638	$141.06	$141.05	$141.10
Purchase #2	$37.57	12.596%	$42.3023	$42.30	$42.30	$42.30
Purchase #3	$179.74	3.152%	$185.4054	$185.41	$185.40	$185.40
Purchase #4	$123.57	12.247%	$138.7036	$138.70	$138.70	$138.70
Purchase #5	$36.30	8.316%	$39.3187	$39.32	$39.30	$39.30
Purchase #6	$154.43	11.753%	$172.5802	$172.58	$172.60	$172.60
Purchase #7	$115.76	3.856%	$120.2237	$120.22	$120.20	$120.20
7 purchase totals =	$781.00		$839.5977	$839.59	$839.55	$839.60