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	$139.54	9.305%	$152.5242	$152.52	$152.50	$152.50
Purchase #2	$149.99	11.836%	$167.7428	$167.74	$167.75	$167.70
Purchase #3	$175.34	8.132%	$189.5986	$189.60	$189.60	$189.60
Purchase #4	$74.33	7.477%	$79.8877	$79.89	$79.90	$79.90
Purchase #5	$127.77	12.255%	$143.4282	$143.43	$143.45	$143.40
Purchase #6	$95.82	11.356%	$106.7013	$106.70	$106.70	$106.70
Purchase #7	$30.59	6.242%	$32.4994	$32.50	$32.50	$32.50
7 purchase totals =	$793.38		$872.3822	$872.38	$872.40	$872.30