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	$73.39	7.491%	$78.8876	$78.89	$78.90	$78.90
Purchase #2	$74.74	6.238%	$79.4023	$79.40	$79.40	$79.40
Purchase #3	$170.38	10.714%	$188.6345	$188.63	$188.65	$188.60
Purchase #4	$95.34	10.358%	$105.2153	$105.22	$105.20	$105.20
Purchase #5	$65.92	8.283%	$71.3802	$71.38	$71.40	$71.40
Purchase #6	$30.84	7.268%	$33.0815	$33.08	$33.10	$33.10
Purchase #7	$91.27	4.586%	$95.4556	$95.46	$95.45	$95.50
7 purchase totals =	$601.88		$652.0570	$652.06	$652.10	$652.10