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	$74.88	5.228%	$78.7947	$78.79	$78.80	$78.80
Purchase #2	$81.94	11.762%	$91.5778	$91.58	$91.60	$91.60
Purchase #3	$14.54	10.871%	$16.1206	$16.12	$16.10	$16.10
Purchase #4	$18.45	9.557%	$20.2133	$20.21	$20.20	$20.20
Purchase #5	$170.64	8.466%	$185.0864	$185.09	$185.10	$185.10
Purchase #6	$97.33	3.279%	$100.5215	$100.52	$100.50	$100.50
Purchase #7	$210.28	7.347%	$225.7293	$225.73	$225.75	$225.70
7 purchase totals =	$668.06		$718.0436	$718.04	$718.05	$718.00