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	$19.61	13.822%	$22.3205	$22.32	$22.30	$22.30
Purchase #2	$149.36	11.322%	$166.2705	$166.27	$166.25	$166.30
Purchase #3	$106.60	9.145%	$116.3486	$116.35	$116.35	$116.30
Purchase #4	$127.72	4.314%	$133.2298	$133.23	$133.25	$133.20
Purchase #5	$200.71	5.390%	$211.5283	$211.53	$211.55	$211.50
Purchase #6	$37.61	11.328%	$41.8705	$41.87	$41.85	$41.90
Purchase #7	$199.33	3.367%	$206.0414	$206.04	$206.05	$206.00
7 purchase totals =	$840.94		$897.6096	$897.61	$897.60	$897.50