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	$102.58	9.505%	$112.3302	$112.33	$112.35	$112.30
Purchase #2	$118.67	9.653%	$130.1252	$130.13	$130.15	$130.10
Purchase #3	$144.85	12.614%	$163.1214	$163.12	$163.10	$163.10
Purchase #4	$123.40	11.145%	$137.1529	$137.15	$137.15	$137.20
Purchase #5	$135.76	7.553%	$146.014	$146.01	$146.00	$146.00
Purchase #6	$72.62	13.424%	$82.3685	$82.37	$82.35	$82.40
Purchase #7	$97.95	13.820%	$111.4867	$111.49	$111.50	$111.50
7 purchase totals =	$795.83		$882.5989	$882.60	$882.60	$882.60