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	$32.73	7.660%	$35.2371	$35.24	$35.25	$35.20
Purchase #2	$128.45	6.310%	$136.5552	$136.56	$136.55	$136.60
Purchase #3	$205.47	9.350%	$224.6814	$224.68	$224.70	$224.70
Purchase #4	$12.93	5.776%	$13.6768	$13.68	$13.70	$13.70
Purchase #5	$41.36	10.689%	$45.781	$45.78	$45.80	$45.80
Purchase #6	$92.27	13.614%	$104.8316	$104.83	$104.85	$104.80
Purchase #7	$100.75	4.423%	$105.2062	$105.21	$105.20	$105.20
7 purchase totals =	$613.96		$665.9693	$665.98	$666.05	$666.00