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	$240.70	10.543%	$266.077	$266.08	$266.10	$266.10
Purchase #2	$90.49	9.672%	$99.2422	$99.24	$99.25	$99.20
Purchase #3	$28.90	11.793%	$32.3082	$32.31	$32.30	$32.30
Purchase #4	$250.69	9.349%	$274.127	$274.13	$274.15	$274.10
Purchase #5	$150.99	5.282%	$158.9653	$158.97	$158.95	$159.00
Purchase #6	$222.42	10.419%	$245.5939	$245.59	$245.60	$245.60
Purchase #7	$230.66	13.668%	$262.1866	$262.19	$262.20	$262.20
7 purchase totals =	$1,214.85		$1,338.5002	$1,338.51	$1,338.55	$1,338.50