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	$219.41	4.609%	$229.5226	$229.52	$229.50	$229.50
Purchase #2	$95.31	5.745%	$100.7856	$100.79	$100.80	$100.80
Purchase #3	$92.66	9.636%	$101.5887	$101.59	$101.60	$101.60
Purchase #4	$52.42	8.236%	$56.7373	$56.74	$56.75	$56.70
Purchase #5	$116.80	12.465%	$131.3591	$131.36	$131.35	$131.40
Purchase #6	$31.81	9.706%	$34.8975	$34.90	$34.90	$34.90
Purchase #7	$163.94	12.478%	$184.3964	$184.40	$184.40	$184.40
7 purchase totals =	$772.35		$839.2872	$839.30	$839.30	$839.30