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	$217.87	4.597%	$227.8855	$227.89	$227.90	$227.90
Purchase #2	$30.45	7.405%	$32.7048	$32.70	$32.70	$32.70
Purchase #3	$72.38	13.104%	$81.8647	$81.86	$81.85	$81.90
Purchase #4	$46.81	13.533%	$53.1448	$53.14	$53.15	$53.10
Purchase #5	$175.56	8.628%	$190.7073	$190.71	$190.70	$190.70
Purchase #6	$9.83	5.444%	$10.3651	$10.37	$10.35	$10.40
Purchase #7	$31.90	4.245%	$33.2542	$33.25	$33.25	$33.30
7 purchase totals =	$584.80		$629.9264	$629.92	$629.90	$630.00