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	$104.59	6.279%	$111.1572	$111.16	$111.15	$111.20
Purchase #2	$171.49	7.184%	$183.8098	$183.81	$183.80	$183.80
Purchase #3	$205.72	4.260%	$214.4837	$214.48	$214.50	$214.50
Purchase #4	$61.88	6.479%	$65.8892	$65.89	$65.90	$65.90
Purchase #5	$74.46	3.860%	$77.3342	$77.33	$77.35	$77.30
Purchase #6	$139.90	9.262%	$152.8575	$152.86	$152.85	$152.90
Purchase #7	$141.91	9.219%	$154.9927	$154.99	$155.00	$155.00
7 purchase totals =	$899.95		$960.5243	$960.52	$960.55	$960.60