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	$142.61	4.130%	$148.4998	$148.50	$148.50	$148.50
Purchase #2	$17.50	4.832%	$18.3456	$18.35	$18.35	$18.30
Purchase #3	$149.44	4.569%	$156.2679	$156.27	$156.25	$156.30
Purchase #4	$19.92	8.201%	$21.5536	$21.55	$21.55	$21.60
Purchase #5	$30.52	7.166%	$32.7071	$32.71	$32.70	$32.70
Purchase #6	$65.45	10.290%	$72.1848	$72.18	$72.20	$72.20
Purchase #7	$93.45	5.848%	$98.915	$98.92	$98.90	$98.90
7 purchase totals =	$518.89		$548.4738	$548.48	$548.45	$548.50