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	$223.48	12.584%	$251.6027	$251.60	$251.60	$251.60
Purchase #2	$33.51	5.789%	$35.4499	$35.45	$35.45	$35.40
Purchase #3	$220.78	8.722%	$240.0364	$240.04	$240.05	$240.00
Purchase #4	$224.73	7.640%	$241.8994	$241.90	$241.90	$241.90
Purchase #5	$123.98	12.781%	$139.8259	$139.83	$139.85	$139.80
Purchase #6	$210.69	4.156%	$219.4463	$219.45	$219.45	$219.40
Purchase #7	$210.67	7.813%	$227.1296	$227.13	$227.15	$227.10
7 purchase totals =	$1,247.84		$1,355.3902	$1,355.40	$1,355.45	$1,355.20