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	$246.54	6.626%	$262.8757	$262.88	$262.90	$262.90
Purchase #2	$129.90	7.513%	$139.6594	$139.66	$139.65	$139.70
Purchase #3	$34.81	7.823%	$37.5332	$37.53	$37.55	$37.50
Purchase #4	$19.29	5.791%	$20.4071	$20.41	$20.40	$20.40
Purchase #5	$123.75	3.662%	$128.2817	$128.28	$128.30	$128.30
Purchase #6	$128.85	5.151%	$135.4871	$135.49	$135.50	$135.50
Purchase #7	$105.86	5.520%	$111.7035	$111.70	$111.70	$111.70
7 purchase totals =	$789.00		$835.9477	$835.95	$836.00	$836.00