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	$65.90	9.298%	$72.0274	$72.03	$72.05	$72.00
Purchase #2	$215.62	12.845%	$243.3164	$243.32	$243.30	$243.30
Purchase #3	$86.27	12.290%	$96.8726	$96.87	$96.85	$96.90
Purchase #4	$141.54	9.574%	$155.091	$155.09	$155.10	$155.10
Purchase #5	$135.54	4.652%	$141.8453	$141.85	$141.85	$141.80
Purchase #6	$111.83	13.776%	$127.2357	$127.24	$127.25	$127.20
Purchase #7	$73.74	8.412%	$79.943	$79.94	$79.95	$79.90
7 purchase totals =	$830.44		$916.3314	$916.34	$916.35	$916.20