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	$138.92	5.280%	$146.255	$146.26	$146.25	$146.30
Purchase #2	$15.59	11.741%	$17.4204	$17.42	$17.40	$17.40
Purchase #3	$90.84	11.521%	$101.3057	$101.31	$101.30	$101.30
Purchase #4	$188.56	6.570%	$200.9484	$200.95	$200.95	$200.90
Purchase #5	$87.43	9.379%	$95.6301	$95.63	$95.65	$95.60
Purchase #6	$103.37	12.480%	$116.2706	$116.27	$116.25	$116.30
Purchase #7	$189.54	10.201%	$208.875	$208.88	$208.90	$208.90
7 purchase totals =	$814.25		$886.7052	$886.72	$886.70	$886.70