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	$109.67	10.748%	$121.4573	$121.46	$121.45	$121.50
Purchase #2	$175.89	11.787%	$196.6222	$196.62	$196.60	$196.60
Purchase #3	$116.45	8.668%	$126.5439	$126.54	$126.55	$126.50
Purchase #4	$101.28	4.525%	$105.8629	$105.86	$105.85	$105.90
Purchase #5	$126.97	9.712%	$139.3013	$139.30	$139.30	$139.30
Purchase #6	$223.43	8.365%	$242.1199	$242.12	$242.10	$242.10
Purchase #7	$190.29	12.768%	$214.5862	$214.59	$214.60	$214.60
7 purchase totals =	$1,043.98		$1,146.4937	$1,146.49	$1,146.45	$1,146.50