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	$201.54	10.401%	$222.5022	$222.50	$222.50	$222.50
Purchase #2	$189.30	3.281%	$195.5109	$195.51	$195.50	$195.50
Purchase #3	$130.55	10.691%	$144.5071	$144.51	$144.50	$144.50
Purchase #4	$211.92	13.644%	$240.8344	$240.83	$240.85	$240.80
Purchase #5	$166.80	3.632%	$172.8582	$172.86	$172.85	$172.90
Purchase #6	$125.92	3.710%	$130.5916	$130.59	$130.60	$130.60
Purchase #7	$114.29	7.250%	$122.576	$122.58	$122.60	$122.60
7 purchase totals =	$1,140.32		$1,229.3804	$1,229.38	$1,229.40	$1,229.40