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	$110.59	5.253%	$116.3993	$116.40	$116.40	$116.40
Purchase #2	$128.50	13.320%	$145.6162	$145.62	$145.60	$145.60
Purchase #3	$41.98	11.532%	$46.8211	$46.82	$46.80	$46.80
Purchase #4	$164.81	8.439%	$178.7183	$178.72	$178.70	$178.70
Purchase #5	$62.33	4.347%	$65.0395	$65.04	$65.05	$65.00
Purchase #6	$147.60	5.507%	$155.7283	$155.73	$155.75	$155.70
Purchase #7	$154.98	11.188%	$172.3192	$172.32	$172.30	$172.30
7 purchase totals =	$810.79		$880.6419	$880.65	$880.60	$880.50