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	$75.73	3.661%	$78.5025	$78.50	$78.50	$78.50
Purchase #2	$54.78	3.425%	$56.6562	$56.66	$56.65	$56.70
Purchase #3	$212.84	5.353%	$224.2333	$224.23	$224.25	$224.20
Purchase #4	$45.95	11.869%	$51.4038	$51.40	$51.40	$51.40
Purchase #5	$128.77	13.276%	$145.8655	$145.87	$145.85	$145.90
Purchase #6	$78.31	6.113%	$83.0971	$83.10	$83.10	$83.10
Purchase #7	$14.72	5.232%	$15.4902	$15.49	$15.50	$15.50
7 purchase totals =	$611.10		$655.2486	$655.25	$655.25	$655.30