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	$79.87	12.669%	$89.9887	$89.99	$90.00	$90.00
Purchase #2	$163.93	12.675%	$184.7081	$184.71	$184.70	$184.70
Purchase #3	$130.50	12.567%	$146.8999	$146.90	$146.90	$146.90
Purchase #4	$86.86	13.772%	$98.8224	$98.82	$98.80	$98.80
Purchase #5	$152.25	8.573%	$165.3024	$165.30	$165.30	$165.30
Purchase #6	$90.57	10.230%	$99.8353	$99.84	$99.85	$99.80
Purchase #7	$243.91	9.577%	$267.2693	$267.27	$267.25	$267.30
7 purchase totals =	$947.89		$1,052.8261	$1,052.83	$1,052.80	$1,052.80