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	$30.48	11.289%	$33.9209	$33.92	$33.90	$33.90
Purchase #2	$238.99	12.388%	$268.5961	$268.60	$268.60	$268.60
Purchase #3	$236.79	4.849%	$248.2719	$248.27	$248.25	$248.30
Purchase #4	$187.38	6.733%	$199.9963	$200.00	$200.00	$200.00
Purchase #5	$226.92	6.846%	$242.4549	$242.45	$242.45	$242.50
Purchase #6	$54.42	13.814%	$61.9376	$61.94	$61.95	$61.90
Purchase #7	$132.33	6.583%	$141.0413	$141.04	$141.05	$141.00
7 purchase totals =	$1,107.31		$1,196.2190	$1,196.22	$1,196.20	$1,196.20