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	$106.87	4.223%	$111.3831	$111.38	$111.40	$111.40
Purchase #2	$239.83	6.435%	$255.2631	$255.26	$255.25	$255.30
Purchase #3	$111.93	8.706%	$121.6746	$121.67	$121.65	$121.70
Purchase #4	$142.96	6.772%	$152.6413	$152.64	$152.65	$152.60
Purchase #5	$212.88	4.466%	$222.3872	$222.39	$222.40	$222.40
Purchase #6	$149.75	8.269%	$162.1328	$162.13	$162.15	$162.10
Purchase #7	$57.59	13.712%	$65.4867	$65.49	$65.50	$65.50
7 purchase totals =	$1,021.81		$1,090.9688	$1,090.96	$1,091.00	$1,091.00