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	$135.31	13.310%	$153.3198	$153.32	$153.30	$153.30
Purchase #2	$90.30	6.594%	$96.2544	$96.25	$96.25	$96.30
Purchase #3	$228.66	5.111%	$240.3468	$240.35	$240.35	$240.30
Purchase #4	$40.32	4.211%	$42.0179	$42.02	$42.00	$42.00
Purchase #5	$122.59	4.497%	$128.1029	$128.10	$128.10	$128.10
Purchase #6	$99.63	10.787%	$110.3771	$110.38	$110.40	$110.40
Purchase #7	$208.85	7.553%	$224.6244	$224.62	$224.60	$224.60
7 purchase totals =	$925.66		$995.0433	$995.04	$995.00	$995.00