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	$107.34	10.371%	$118.4722	$118.47	$118.45	$118.50
Purchase #2	$217.31	11.323%	$241.916	$241.92	$241.90	$241.90
Purchase #3	$18.32	7.755%	$19.7407	$19.74	$19.75	$19.70
Purchase #4	$123.51	5.300%	$130.056	$130.06	$130.05	$130.10
Purchase #5	$38.79	11.450%	$43.2315	$43.23	$43.25	$43.20
Purchase #6	$99.74	5.717%	$105.4421	$105.44	$105.45	$105.40
Purchase #7	$73.62	5.759%	$77.8598	$77.86	$77.85	$77.90
7 purchase totals =	$678.63		$736.7183	$736.72	$736.70	$736.70