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	$96.64	3.781%	$100.294	$100.29	$100.30	$100.30
Purchase #2	$75.95	8.178%	$82.1612	$82.16	$82.15	$82.20
Purchase #3	$51.45	6.816%	$54.9568	$54.96	$54.95	$55.00
Purchase #4	$128.49	13.827%	$146.2563	$146.26	$146.25	$146.30
Purchase #5	$200.37	13.104%	$226.6265	$226.63	$226.65	$226.60
Purchase #6	$30.87	5.113%	$32.4484	$32.45	$32.45	$32.40
Purchase #7	$6.83	8.121%	$7.3847	$7.38	$7.40	$7.40
7 purchase totals =	$590.60		$650.1279	$650.13	$650.15	$650.20