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	$54.59	12.308%	$61.3089	$61.31	$61.30	$61.30
Purchase #2	$57.26	12.580%	$64.4633	$64.46	$64.45	$64.50
Purchase #3	$24.80	10.661%	$27.4439	$27.44	$27.45	$27.40
Purchase #4	$70.35	10.831%	$77.9696	$77.97	$77.95	$78.00
Purchase #5	$238.42	9.494%	$261.0556	$261.06	$261.05	$261.10
Purchase #6	$77.86	3.718%	$80.7548	$80.75	$80.75	$80.80
Purchase #7	$103.77	12.653%	$116.9	$116.90	$116.90	$116.90
7 purchase totals =	$627.05		$689.8961	$689.89	$689.85	$690.00