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	$215.72	8.422%	$233.8879	$233.89	$233.90	$233.90
Purchase #2	$124.92	13.535%	$141.8279	$141.83	$141.85	$141.80
Purchase #3	$130.34	9.778%	$143.0846	$143.08	$143.10	$143.10
Purchase #4	$81.27	3.148%	$83.8284	$83.83	$83.85	$83.80
Purchase #5	$42.39	6.574%	$45.1767	$45.18	$45.20	$45.20
Purchase #6	$60.66	6.174%	$64.4051	$64.41	$64.40	$64.40
Purchase #7	$127.93	5.731%	$135.2617	$135.26	$135.25	$135.30
7 purchase totals =	$783.23		$847.4723	$847.48	$847.55	$847.50