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	$49.82	6.146%	$52.8819	$52.88	$52.90	$52.90
Purchase #2	$17.60	4.137%	$18.3281	$18.33	$18.35	$18.30
Purchase #3	$187.79	11.465%	$209.3201	$209.32	$209.30	$209.30
Purchase #4	$34.77	11.712%	$38.8423	$38.84	$38.85	$38.80
Purchase #5	$153.69	9.740%	$168.6594	$168.66	$168.65	$168.70
Purchase #6	$132.25	5.685%	$139.7684	$139.77	$139.75	$139.80
Purchase #7	$48.44	9.190%	$52.8916	$52.89	$52.90	$52.90
7 purchase totals =	$624.36		$680.6918	$680.69	$680.70	$680.70