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	$131.64	11.660%	$146.9892	$146.99	$147.00	$147.00
Purchase #2	$115.39	4.273%	$120.3206	$120.32	$120.30	$120.30
Purchase #3	$123.61	11.645%	$138.0044	$138.00	$138.00	$138.00
Purchase #4	$242.91	10.577%	$268.6026	$268.60	$268.60	$268.60
Purchase #5	$81.85	9.742%	$89.8238	$89.82	$89.80	$89.80
Purchase #6	$129.32	9.435%	$141.5213	$141.52	$141.50	$141.50
Purchase #7	$37.31	13.111%	$42.2017	$42.20	$42.20	$42.20
7 purchase totals =	$862.03		$947.4636	$947.45	$947.40	$947.40