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	$121.79	8.822%	$132.5343	$132.53	$132.55	$132.50
Purchase #2	$247.92	3.208%	$255.8733	$255.87	$255.85	$255.90
Purchase #3	$154.87	3.673%	$160.5584	$160.56	$160.55	$160.60
Purchase #4	$48.73	10.376%	$53.7862	$53.79	$53.80	$53.80
Purchase #5	$83.33	7.209%	$89.3373	$89.34	$89.35	$89.30
Purchase #6	$42.85	11.329%	$47.7045	$47.70	$47.70	$47.70
Purchase #7	$144.40	3.481%	$149.4266	$149.43	$149.45	$149.40
7 purchase totals =	$843.89		$889.2206	$889.22	$889.25	$889.20