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	$85.28	5.843%	$90.2629	$90.26	$90.25	$90.30
Purchase #2	$187.45	9.394%	$205.0591	$205.06	$205.05	$205.10
Purchase #3	$119.90	11.801%	$134.0494	$134.05	$134.05	$134.00
Purchase #4	$95.77	4.457%	$100.0385	$100.04	$100.05	$100.00
Purchase #5	$102.71	8.837%	$111.7865	$111.79	$111.80	$111.80
Purchase #6	$160.47	7.855%	$173.0749	$173.07	$173.05	$173.10
Purchase #7	$56.30	6.107%	$59.7382	$59.74	$59.75	$59.70
7 purchase totals =	$807.88		$874.0095	$874.01	$874.00	$874.00