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	$45.98	10.130%	$50.6378	$50.64	$50.65	$50.60
Purchase #2	$76.62	12.596%	$86.2711	$86.27	$86.25	$86.30
Purchase #3	$234.82	13.431%	$266.3587	$266.36	$266.35	$266.40
Purchase #4	$123.92	10.799%	$137.3021	$137.30	$137.30	$137.30
Purchase #5	$226.83	10.866%	$251.4773	$251.48	$251.50	$251.50
Purchase #6	$40.48	11.529%	$45.1469	$45.15	$45.15	$45.10
Purchase #7	$32.32	6.203%	$34.3248	$34.32	$34.30	$34.30
7 purchase totals =	$780.97		$871.5187	$871.52	$871.50	$871.50