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	$129.30	6.489%	$137.6903	$137.69	$137.70	$137.70
Purchase #2	$166.67	11.284%	$185.477	$185.48	$185.50	$185.50
Purchase #3	$149.54	10.377%	$165.0578	$165.06	$165.05	$165.10
Purchase #4	$10.84	8.748%	$11.7883	$11.79	$11.80	$11.80
Purchase #5	$48.69	6.543%	$51.8758	$51.88	$51.90	$51.90
Purchase #6	$41.30	9.319%	$45.1487	$45.15	$45.15	$45.10
Purchase #7	$31.94	6.189%	$33.9168	$33.92	$33.90	$33.90
7 purchase totals =	$578.28		$630.9547	$630.97	$631.00	$631.00