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	$46.52	7.417%	$49.9704	$49.97	$49.95	$50.00
Purchase #2	$142.63	4.563%	$149.1382	$149.14	$149.15	$149.10
Purchase #3	$13.96	12.798%	$15.7466	$15.75	$15.75	$15.70
Purchase #4	$184.78	6.346%	$196.5061	$196.51	$196.50	$196.50
Purchase #5	$131.32	6.218%	$139.4855	$139.49	$139.50	$139.50
Purchase #6	$124.79	5.207%	$131.2878	$131.29	$131.30	$131.30
Purchase #7	$75.55	13.416%	$85.6858	$85.69	$85.70	$85.70
7 purchase totals =	$719.55		$767.8204	$767.84	$767.85	$767.80