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	$72.58	12.462%	$81.6249	$81.62	$81.60	$81.60
Purchase #2	$38.95	8.515%	$42.2666	$42.27	$42.25	$42.30
Purchase #3	$76.94	10.827%	$85.2703	$85.27	$85.25	$85.30
Purchase #4	$139.89	3.695%	$145.0589	$145.06	$145.05	$145.10
Purchase #5	$46.25	6.610%	$49.3071	$49.31	$49.30	$49.30
Purchase #6	$244.44	4.653%	$255.8138	$255.81	$255.80	$255.80
Purchase #7	$186.46	13.751%	$212.1001	$212.10	$212.10	$212.10
7 purchase totals =	$805.51		$871.4417	$871.44	$871.35	$871.50