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	$29.62	10.209%	$32.6439	$32.64	$32.65	$32.60
Purchase #2	$149.25	11.781%	$166.8331	$166.83	$166.85	$166.80
Purchase #3	$210.34	3.794%	$218.3203	$218.32	$218.30	$218.30
Purchase #4	$100.83	4.423%	$105.2897	$105.29	$105.30	$105.30
Purchase #5	$72.38	6.586%	$77.1469	$77.15	$77.15	$77.10
Purchase #6	$172.50	10.595%	$190.7764	$190.78	$190.80	$190.80
Purchase #7	$172.97	9.453%	$189.3209	$189.32	$189.30	$189.30
7 purchase totals =	$907.89		$980.3312	$980.33	$980.35	$980.20