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	$37.58	11.250%	$41.8078	$41.81	$41.80	$41.80
Purchase #2	$163.59	5.661%	$172.8508	$172.85	$172.85	$172.90
Purchase #3	$147.43	13.158%	$166.8288	$166.83	$166.85	$166.80
Purchase #4	$126.39	9.449%	$138.3326	$138.33	$138.35	$138.30
Purchase #5	$162.37	6.311%	$172.6172	$172.62	$172.60	$172.60
Purchase #6	$73.66	8.268%	$79.7502	$79.75	$79.75	$79.80
Purchase #7	$227.86	12.171%	$255.5928	$255.59	$255.60	$255.60
7 purchase totals =	$938.88		$1,027.7802	$1,027.78	$1,027.80	$1,027.80