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	$136.42	10.211%	$150.3498	$150.35	$150.35	$150.30
Purchase #2	$212.47	12.299%	$238.6017	$238.60	$238.60	$238.60
Purchase #3	$130.59	12.395%	$146.7766	$146.78	$146.80	$146.80
Purchase #4	$144.36	7.732%	$155.5219	$155.52	$155.50	$155.50
Purchase #5	$79.91	12.147%	$89.6167	$89.62	$89.60	$89.60
Purchase #6	$209.88	4.181%	$218.6551	$218.66	$218.65	$218.70
Purchase #7	$124.25	7.810%	$133.9539	$133.95	$133.95	$134.00
7 purchase totals =	$1,037.88		$1,133.4757	$1,133.48	$1,133.45	$1,133.50