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	$95.53	9.201%	$104.3197	$104.32	$104.30	$104.30
Purchase #2	$154.90	12.842%	$174.7923	$174.79	$174.80	$174.80
Purchase #3	$141.37	12.299%	$158.7571	$158.76	$158.75	$158.80
Purchase #4	$214.26	12.660%	$241.3853	$241.39	$241.40	$241.40
Purchase #5	$159.98	7.616%	$172.1641	$172.16	$172.15	$172.20
Purchase #6	$190.84	9.257%	$208.5061	$208.51	$208.50	$208.50
Purchase #7	$44.49	11.144%	$49.448	$49.45	$49.45	$49.40
7 purchase totals =	$1,001.37		$1,109.3726	$1,109.38	$1,109.35	$1,109.40