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	$89.92	10.733%	$99.5711	$99.57	$99.55	$99.60
Purchase #2	$42.51	7.693%	$45.7803	$45.78	$45.80	$45.80
Purchase #3	$56.85	3.509%	$58.8449	$58.84	$58.85	$58.80
Purchase #4	$136.90	11.838%	$153.1062	$153.11	$153.10	$153.10
Purchase #5	$144.66	6.792%	$154.4853	$154.49	$154.50	$154.50
Purchase #6	$188.52	6.865%	$201.4619	$201.46	$201.45	$201.50
Purchase #7	$112.94	5.510%	$119.163	$119.16	$119.15	$119.20
7 purchase totals =	$772.30		$832.4127	$832.41	$832.40	$832.50