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	$122.97	13.134%	$139.1209	$139.12	$139.10	$139.10
Purchase #2	$17.50	5.516%	$18.4653	$18.47	$18.45	$18.50
Purchase #3	$117.92	10.580%	$130.3959	$130.40	$130.40	$130.40
Purchase #4	$41.61	5.719%	$43.9897	$43.99	$44.00	$44.00
Purchase #5	$135.37	9.735%	$148.5483	$148.55	$148.55	$148.50
Purchase #6	$28.83	10.757%	$31.9312	$31.93	$31.95	$31.90
Purchase #7	$90.97	9.735%	$99.8259	$99.83	$99.85	$99.80
7 purchase totals =	$555.17		$612.2772	$612.29	$612.30	$612.20