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	$15.88	13.421%	$18.0113	$18.01	$18.00	$18.00
Purchase #2	$167.37	6.575%	$178.3746	$178.37	$178.35	$178.40
Purchase #3	$149.56	6.264%	$158.9284	$158.93	$158.95	$158.90
Purchase #4	$88.66	13.659%	$100.7701	$100.77	$100.75	$100.80
Purchase #5	$163.98	13.168%	$185.5729	$185.57	$185.55	$185.60
Purchase #6	$115.40	7.827%	$124.4324	$124.43	$124.45	$124.40
Purchase #7	$209.29	6.205%	$222.2764	$222.28	$222.30	$222.30
7 purchase totals =	$910.14		$988.3661	$988.36	$988.35	$988.40