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	$76.99	5.844%	$81.4893	$81.49	$81.50	$81.50
Purchase #2	$26.41	6.857%	$28.2209	$28.22	$28.20	$28.20
Purchase #3	$35.39	5.201%	$37.2306	$37.23	$37.25	$37.20
Purchase #4	$173.40	4.810%	$181.7405	$181.74	$181.75	$181.70
Purchase #5	$231.85	13.583%	$263.3422	$263.34	$263.35	$263.30
Purchase #6	$93.45	7.190%	$100.1691	$100.17	$100.15	$100.20
Purchase #7	$104.59	6.470%	$111.357	$111.36	$111.35	$111.40
7 purchase totals =	$742.08		$803.5496	$803.55	$803.55	$803.50