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	$7.62	3.441%	$7.8822	$7.88	$7.90	$7.90
Purchase #2	$65.35	10.157%	$71.9876	$71.99	$72.00	$72.00
Purchase #3	$137.33	4.645%	$143.709	$143.71	$143.70	$143.70
Purchase #4	$106.39	13.106%	$120.3335	$120.33	$120.35	$120.30
Purchase #5	$26.92	5.419%	$28.3788	$28.38	$28.40	$28.40
Purchase #6	$77.38	10.631%	$85.6063	$85.61	$85.60	$85.60
Purchase #7	$76.83	6.262%	$81.6411	$81.64	$81.65	$81.60
7 purchase totals =	$497.82		$539.5385	$539.54	$539.60	$539.50