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	$224.56	6.257%	$238.6107	$238.61	$238.60	$238.60
Purchase #2	$146.85	5.540%	$154.9855	$154.99	$155.00	$155.00
Purchase #3	$235.55	12.211%	$264.313	$264.31	$264.30	$264.30
Purchase #4	$8.84	3.564%	$9.1551	$9.16	$9.15	$9.20
Purchase #5	$35.88	11.556%	$40.0263	$40.03	$40.05	$40.00
Purchase #6	$123.90	11.834%	$138.5623	$138.56	$138.55	$138.60
Purchase #7	$228.47	11.642%	$255.0685	$255.07	$255.05	$255.10
7 purchase totals =	$1,004.05		$1,100.7214	$1,100.73	$1,100.70	$1,100.80