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	$29.37	11.145%	$32.6433	$32.64	$32.65	$32.60
Purchase #2	$44.34	9.732%	$48.6552	$48.66	$48.65	$48.70
Purchase #3	$34.73	10.759%	$38.4666	$38.47	$38.45	$38.50
Purchase #4	$70.70	10.768%	$78.313	$78.31	$78.30	$78.30
Purchase #5	$227.42	6.107%	$241.3085	$241.31	$241.30	$241.30
Purchase #6	$73.31	13.693%	$83.3483	$83.35	$83.35	$83.30
Purchase #7	$27.59	9.784%	$30.2894	$30.29	$30.30	$30.30
7 purchase totals =	$507.46		$553.0243	$553.03	$553.00	$553.00