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	$13.85	12.476%	$15.5779	$15.58	$15.60	$15.60
Purchase #2	$45.51	5.254%	$47.9011	$47.90	$47.90	$47.90
Purchase #3	$236.82	4.853%	$248.3129	$248.31	$248.30	$248.30
Purchase #4	$126.98	13.197%	$143.7376	$143.74	$143.75	$143.70
Purchase #5	$9.85	6.782%	$10.518	$10.52	$10.50	$10.50
Purchase #6	$233.70	13.202%	$264.5531	$264.55	$264.55	$264.60
Purchase #7	$96.90	3.546%	$100.3361	$100.34	$100.35	$100.30
7 purchase totals =	$763.61		$830.9367	$830.94	$830.95	$830.90