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	$175.48	4.567%	$183.4942	$183.49	$183.50	$183.50
Purchase #2	$131.83	6.434%	$140.3119	$140.31	$140.30	$140.30
Purchase #3	$94.49	5.344%	$99.5395	$99.54	$99.55	$99.50
Purchase #4	$170.32	9.716%	$186.8683	$186.87	$186.85	$186.90
Purchase #5	$10.94	10.197%	$12.0556	$12.06	$12.05	$12.10
Purchase #6	$180.57	7.762%	$194.5858	$194.59	$194.60	$194.60
Purchase #7	$219.26	4.290%	$228.6663	$228.67	$228.65	$228.70
7 purchase totals =	$982.89		$1,045.5216	$1,045.53	$1,045.50	$1,045.60