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	$28.71	9.633%	$31.4756	$31.48	$31.50	$31.50
Purchase #2	$221.81	11.298%	$246.8701	$246.87	$246.85	$246.90
Purchase #3	$177.84	3.412%	$183.9079	$183.91	$183.90	$183.90
Purchase #4	$105.57	5.428%	$111.3003	$111.30	$111.30	$111.30
Purchase #5	$16.43	7.668%	$17.6899	$17.69	$17.70	$17.70
Purchase #6	$34.78	8.298%	$37.666	$37.67	$37.65	$37.70
Purchase #7	$42.42	6.789%	$45.2999	$45.30	$45.30	$45.30
7 purchase totals =	$627.56		$674.2097	$674.22	$674.20	$674.30