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	$241.74	13.474%	$274.312	$274.31	$274.30	$274.30
Purchase #2	$241.31	5.187%	$253.8267	$253.83	$253.85	$253.80
Purchase #3	$224.90	10.545%	$248.6157	$248.62	$248.60	$248.60
Purchase #4	$59.48	3.866%	$61.7795	$61.78	$61.80	$61.80
Purchase #5	$91.28	8.822%	$99.3327	$99.33	$99.35	$99.30
Purchase #6	$137.47	4.196%	$143.2382	$143.24	$143.25	$143.20
Purchase #7	$187.49	6.443%	$199.57	$199.57	$199.55	$199.60
7 purchase totals =	$1,183.67		$1,280.6748	$1,280.68	$1,280.70	$1,280.60