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	$29.33	7.388%	$31.4969	$31.50	$31.50	$31.50
Purchase #2	$162.41	3.268%	$167.7176	$167.72	$167.70	$167.70
Purchase #3	$12.28	8.427%	$13.3148	$13.31	$13.30	$13.30
Purchase #4	$6.40	11.559%	$7.1398	$7.14	$7.15	$7.10
Purchase #5	$100.36	4.224%	$104.5992	$104.60	$104.60	$104.60
Purchase #6	$16.43	10.650%	$18.1798	$18.18	$18.20	$18.20
Purchase #7	$42.37	3.802%	$43.9809	$43.98	$44.00	$44.00
7 purchase totals =	$369.58		$386.4290	$386.43	$386.45	$386.40