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	$33.92	10.861%	$37.6041	$37.60	$37.60	$37.60
Purchase #2	$142.89	12.514%	$160.7713	$160.77	$160.75	$160.80
Purchase #3	$59.52	3.262%	$61.4615	$61.46	$61.45	$61.50
Purchase #4	$154.60	10.847%	$171.3695	$171.37	$171.35	$171.40
Purchase #5	$108.95	8.269%	$117.9591	$117.96	$117.95	$118.00
Purchase #6	$130.71	9.310%	$142.8791	$142.88	$142.90	$142.90
Purchase #7	$70.32	13.486%	$79.8034	$79.80	$79.80	$79.80
7 purchase totals =	$700.91		$771.8480	$771.84	$771.80	$772.00