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	$124.92	11.181%	$138.8873	$138.89	$138.90	$138.90
Purchase #2	$89.73	13.191%	$101.5663	$101.57	$101.55	$101.60
Purchase #3	$31.66	4.157%	$32.9761	$32.98	$33.00	$33.00
Purchase #4	$202.44	11.605%	$225.9332	$225.93	$225.95	$225.90
Purchase #5	$127.82	12.178%	$143.3859	$143.39	$143.40	$143.40
Purchase #6	$100.32	5.247%	$105.5838	$105.58	$105.60	$105.60
Purchase #7	$54.26	11.586%	$60.5466	$60.55	$60.55	$60.50
7 purchase totals =	$731.15		$808.8792	$808.89	$808.95	$808.90