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	$42.49	8.777%	$46.2193	$46.22	$46.20	$46.20
Purchase #2	$213.88	10.597%	$236.5449	$236.54	$236.55	$236.50
Purchase #3	$87.42	4.559%	$91.4055	$91.41	$91.40	$91.40
Purchase #4	$60.73	5.846%	$64.2803	$64.28	$64.30	$64.30
Purchase #5	$91.84	9.839%	$100.8761	$100.88	$100.90	$100.90
Purchase #6	$40.33	8.751%	$43.8593	$43.86	$43.85	$43.90
Purchase #7	$32.25	5.253%	$33.9441	$33.94	$33.95	$33.90
7 purchase totals =	$568.94		$617.1295	$617.13	$617.15	$617.10