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	$219.56	6.729%	$234.3342	$234.33	$234.35	$234.30
Purchase #2	$242.93	10.154%	$267.5971	$267.60	$267.60	$267.60
Purchase #3	$40.52	12.680%	$45.6579	$45.66	$45.65	$45.70
Purchase #4	$68.93	11.569%	$76.9045	$76.90	$76.90	$76.90
Purchase #5	$123.48	6.564%	$131.5852	$131.59	$131.60	$131.60
Purchase #6	$182.32	7.422%	$195.8518	$195.85	$195.85	$195.90
Purchase #7	$18.80	7.153%	$20.1448	$20.14	$20.15	$20.10
7 purchase totals =	$896.54		$972.0755	$972.07	$972.10	$972.10