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	$41.51	7.163%	$44.4834	$44.48	$44.50	$44.50
Purchase #2	$133.76	13.367%	$151.6397	$151.64	$151.65	$151.60
Purchase #3	$89.93	10.637%	$99.4959	$99.50	$99.50	$99.50
Purchase #4	$192.96	8.385%	$209.1397	$209.14	$209.15	$209.10
Purchase #5	$24.58	11.430%	$27.3895	$27.39	$27.40	$27.40
Purchase #6	$231.40	13.551%	$262.757	$262.76	$262.75	$262.80
Purchase #7	$19.64	4.642%	$20.5517	$20.55	$20.55	$20.60
7 purchase totals =	$733.78		$815.4569	$815.46	$815.50	$815.50