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	$81.67	11.634%	$91.1715	$91.17	$91.15	$91.20
Purchase #2	$73.89	7.765%	$79.6276	$79.63	$79.65	$79.60
Purchase #3	$95.36	8.509%	$103.4742	$103.47	$103.45	$103.50
Purchase #4	$144.35	13.701%	$164.1274	$164.13	$164.15	$164.10
Purchase #5	$159.61	4.709%	$167.126	$167.13	$167.15	$167.10
Purchase #6	$243.92	10.393%	$269.2706	$269.27	$269.25	$269.30
Purchase #7	$101.54	3.644%	$105.2401	$105.24	$105.25	$105.20
7 purchase totals =	$900.34		$980.0374	$980.04	$980.05	$980.00