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	$145.41	7.820%	$156.7811	$156.78	$156.80	$156.80
Purchase #2	$77.86	9.388%	$85.1695	$85.17	$85.15	$85.20
Purchase #3	$151.52	7.246%	$162.4991	$162.50	$162.50	$162.50
Purchase #4	$189.32	4.733%	$198.2805	$198.28	$198.30	$198.30
Purchase #5	$44.46	5.166%	$46.7568	$46.76	$46.75	$46.80
Purchase #6	$35.98	6.116%	$38.1805	$38.18	$38.20	$38.20
Purchase #7	$228.41	5.447%	$240.8515	$240.85	$240.85	$240.90
7 purchase totals =	$872.96		$928.5190	$928.52	$928.55	$928.70