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	$21.58	11.657%	$24.0956	$24.10	$24.10	$24.10
Purchase #2	$64.63	10.218%	$71.2339	$71.23	$71.25	$71.20
Purchase #3	$128.46	7.361%	$137.9159	$137.92	$137.90	$137.90
Purchase #4	$65.87	4.438%	$68.7933	$68.79	$68.80	$68.80
Purchase #5	$73.60	13.522%	$83.5522	$83.55	$83.55	$83.60
Purchase #6	$37.45	5.766%	$39.6094	$39.61	$39.60	$39.60
Purchase #7	$82.89	7.754%	$89.3173	$89.32	$89.30	$89.30
7 purchase totals =	$474.48		$514.5176	$514.52	$514.50	$514.50