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	$54.91	10.196%	$60.5086	$60.51	$60.50	$60.50
Purchase #2	$34.35	4.194%	$35.7906	$35.79	$35.80	$35.80
Purchase #3	$241.64	6.865%	$258.2286	$258.23	$258.25	$258.20
Purchase #4	$174.97	5.211%	$184.0877	$184.09	$184.10	$184.10
Purchase #5	$96.35	4.384%	$100.574	$100.57	$100.55	$100.60
Purchase #6	$74.94	9.594%	$82.1297	$82.13	$82.15	$82.10
Purchase #7	$74.98	5.134%	$78.8295	$78.83	$78.85	$78.80
7 purchase totals =	$752.14		$800.1487	$800.15	$800.20	$800.10