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	$192.40	13.357%	$218.0989	$218.10	$218.10	$218.10
Purchase #2	$49.40	7.763%	$53.2349	$53.23	$53.25	$53.20
Purchase #3	$174.38	5.781%	$184.4609	$184.46	$184.45	$184.50
Purchase #4	$72.90	4.708%	$76.3321	$76.33	$76.35	$76.30
Purchase #5	$69.96	9.393%	$76.5313	$76.53	$76.55	$76.50
Purchase #6	$106.59	4.622%	$111.5166	$111.52	$111.50	$111.50
Purchase #7	$49.94	12.224%	$56.0447	$56.04	$56.05	$56.00
7 purchase totals =	$715.57		$776.2194	$776.21	$776.25	$776.10