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	$85.75	9.378%	$93.7916	$93.79	$93.80	$93.80
Purchase #2	$69.55	3.785%	$72.1825	$72.18	$72.20	$72.20
Purchase #3	$100.62	10.506%	$111.1911	$111.19	$111.20	$111.20
Purchase #4	$86.25	13.786%	$98.1404	$98.14	$98.15	$98.10
Purchase #5	$221.35	3.210%	$228.4553	$228.46	$228.45	$228.50
Purchase #6	$18.47	8.840%	$20.1027	$20.10	$20.10	$20.10
Purchase #7	$89.60	6.841%	$95.7295	$95.73	$95.75	$95.70
7 purchase totals =	$671.59		$719.5931	$719.59	$719.65	$719.60