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	$37.75	13.748%	$42.9399	$42.94	$42.95	$42.90
Purchase #2	$96.37	6.585%	$102.716	$102.72	$102.70	$102.70
Purchase #3	$168.86	7.138%	$180.9132	$180.91	$180.90	$180.90
Purchase #4	$182.94	12.466%	$205.7453	$205.75	$205.75	$205.70
Purchase #5	$122.32	11.223%	$136.048	$136.05	$136.05	$136.00
Purchase #6	$224.60	3.856%	$233.2606	$233.26	$233.25	$233.30
Purchase #7	$67.82	13.697%	$77.1093	$77.11	$77.10	$77.10
7 purchase totals =	$900.66		$978.7323	$978.74	$978.70	$978.60