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	$126.37	6.292%	$134.3212	$134.32	$134.30	$134.30
Purchase #2	$21.26	3.724%	$22.0517	$22.05	$22.05	$22.10
Purchase #3	$100.50	3.546%	$104.0637	$104.06	$104.05	$104.10
Purchase #4	$68.59	6.192%	$72.8371	$72.84	$72.85	$72.80
Purchase #5	$74.59	11.253%	$82.9836	$82.98	$83.00	$83.00
Purchase #6	$71.99	13.802%	$81.9261	$81.93	$81.95	$81.90
Purchase #7	$50.92	8.622%	$55.3103	$55.31	$55.30	$55.30
7 purchase totals =	$514.22		$553.4937	$553.49	$553.50	$553.50