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	$53.81	11.555%	$60.0277	$60.03	$60.05	$60.00
Purchase #2	$122.89	12.109%	$137.7708	$137.77	$137.75	$137.80
Purchase #3	$140.32	10.606%	$155.2023	$155.20	$155.20	$155.20
Purchase #4	$92.64	6.341%	$98.5143	$98.51	$98.50	$98.50
Purchase #5	$170.77	8.400%	$185.1147	$185.11	$185.10	$185.10
Purchase #6	$79.27	13.525%	$89.9913	$89.99	$90.00	$90.00
Purchase #7	$155.85	11.426%	$173.6574	$173.66	$173.65	$173.70
7 purchase totals =	$815.55		$900.2785	$900.27	$900.25	$900.30