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	$49.69	7.729%	$53.5305	$53.53	$53.55	$53.50
Purchase #2	$39.93	8.234%	$43.2178	$43.22	$43.20	$43.20
Purchase #3	$65.66	7.835%	$70.8045	$70.80	$70.80	$70.80
Purchase #4	$82.63	5.853%	$87.4663	$87.47	$87.45	$87.50
Purchase #5	$40.57	7.472%	$43.6014	$43.60	$43.60	$43.60
Purchase #6	$124.84	5.240%	$131.3816	$131.38	$131.40	$131.40
Purchase #7	$86.45	5.679%	$91.3595	$91.36	$91.35	$91.40
7 purchase totals =	$489.77		$521.3616	$521.36	$521.35	$521.40