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	$162.28	13.179%	$183.6669	$183.67	$183.65	$183.70
Purchase #2	$167.47	9.621%	$183.5823	$183.58	$183.60	$183.60
Purchase #3	$47.32	12.336%	$53.1574	$53.16	$53.15	$53.20
Purchase #4	$93.46	6.218%	$99.2713	$99.27	$99.25	$99.30
Purchase #5	$20.71	9.626%	$22.7035	$22.70	$22.70	$22.70
Purchase #6	$166.41	12.554%	$187.3011	$187.30	$187.30	$187.30
Purchase #7	$101.87	3.680%	$105.6188	$105.62	$105.60	$105.60
7 purchase totals =	$759.52		$835.3013	$835.30	$835.25	$835.40