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	$132.36	10.748%	$146.5861	$146.59	$146.60	$146.60
Purchase #2	$115.73	12.423%	$130.1071	$130.11	$130.10	$130.10
Purchase #3	$79.50	3.573%	$82.3405	$82.34	$82.35	$82.30
Purchase #4	$177.38	10.255%	$195.5703	$195.57	$195.55	$195.60
Purchase #5	$89.58	13.321%	$101.513	$101.51	$101.50	$101.50
Purchase #6	$91.92	10.522%	$101.5918	$101.59	$101.60	$101.60
Purchase #7	$233.81	5.215%	$246.0032	$246.00	$246.00	$246.00
7 purchase totals =	$920.28		$1,003.7120	$1,003.71	$1,003.70	$1,003.70