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	$95.89	8.703%	$104.2353	$104.24	$104.25	$104.20
Purchase #2	$39.35	6.282%	$41.822	$41.82	$41.80	$41.80
Purchase #3	$96.25	7.374%	$103.3475	$103.35	$103.35	$103.30
Purchase #4	$70.51	9.111%	$76.9342	$76.93	$76.95	$76.90
Purchase #5	$118.50	7.369%	$127.2323	$127.23	$127.25	$127.20
Purchase #6	$40.31	4.162%	$41.9877	$41.99	$42.00	$42.00
Purchase #7	$29.89	10.557%	$33.0455	$33.05	$33.05	$33.00
7 purchase totals =	$490.70		$528.6045	$528.61	$528.65	$528.40