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	$246.51	11.361%	$274.516	$274.52	$274.50	$274.50
Purchase #2	$232.80	11.154%	$258.7665	$258.77	$258.75	$258.80
Purchase #3	$17.40	6.109%	$18.463	$18.46	$18.45	$18.50
Purchase #4	$61.97	7.248%	$66.4616	$66.46	$66.45	$66.50
Purchase #5	$50.49	12.590%	$56.8467	$56.85	$56.85	$56.80
Purchase #6	$130.27	13.210%	$147.4787	$147.48	$147.50	$147.50
Purchase #7	$28.29	13.836%	$32.2042	$32.20	$32.20	$32.20
7 purchase totals =	$767.73		$854.7367	$854.74	$854.70	$854.80