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	$51.95	11.778%	$58.0687	$58.07	$58.05	$58.10
Purchase #2	$95.72	13.683%	$108.8174	$108.82	$108.80	$108.80
Purchase #3	$99.31	10.667%	$109.9034	$109.90	$109.90	$109.90
Purchase #4	$105.38	11.277%	$117.2637	$117.26	$117.25	$117.30
Purchase #5	$192.87	6.334%	$205.0864	$205.09	$205.10	$205.10
Purchase #6	$222.31	7.723%	$239.479	$239.48	$239.50	$239.50
Purchase #7	$155.58	5.810%	$164.6192	$164.62	$164.60	$164.60
7 purchase totals =	$923.12		$1,003.2378	$1,003.24	$1,003.20	$1,003.30