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	$5.56	7.521%	$5.9782	$5.98	$6.00	$6.00
Purchase #2	$164.25	4.810%	$172.1504	$172.15	$172.15	$172.20
Purchase #3	$140.40	9.641%	$153.936	$153.94	$153.95	$153.90
Purchase #4	$238.91	4.426%	$249.4842	$249.48	$249.50	$249.50
Purchase #5	$203.72	9.246%	$222.556	$222.56	$222.55	$222.60
Purchase #6	$140.86	5.550%	$148.6777	$148.68	$148.70	$148.70
Purchase #7	$171.77	11.159%	$190.9378	$190.94	$190.95	$190.90
7 purchase totals =	$1,065.47		$1,143.7203	$1,143.73	$1,143.80	$1,143.80