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	$129.55	8.162%	$140.1239	$140.12	$140.10	$140.10
Purchase #2	$89.76	11.494%	$100.077	$100.08	$100.10	$100.10
Purchase #3	$179.87	6.205%	$191.0309	$191.03	$191.05	$191.00
Purchase #4	$81.88	11.800%	$91.5418	$91.54	$91.55	$91.50
Purchase #5	$40.90	9.410%	$44.7487	$44.75	$44.75	$44.70
Purchase #6	$127.92	11.536%	$142.6769	$142.68	$142.70	$142.70
Purchase #7	$33.47	13.703%	$38.0564	$38.06	$38.05	$38.10
7 purchase totals =	$683.35		$748.2556	$748.26	$748.30	$748.20