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	$81.60	11.746%	$91.1847	$91.18	$91.20	$91.20
Purchase #2	$208.72	10.510%	$230.6565	$230.66	$230.65	$230.70
Purchase #3	$34.54	7.490%	$37.127	$37.13	$37.15	$37.10
Purchase #4	$65.45	3.461%	$67.7152	$67.72	$67.70	$67.70
Purchase #5	$82.67	6.377%	$87.9419	$87.94	$87.95	$87.90
Purchase #6	$135.40	7.557%	$145.6322	$145.63	$145.65	$145.60
Purchase #7	$99.59	6.579%	$106.142	$106.14	$106.15	$106.10
7 purchase totals =	$707.97		$766.3995	$766.40	$766.45	$766.30