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	$34.98	13.842%	$39.8219	$39.82	$39.80	$39.80
Purchase #2	$18.99	9.617%	$20.8163	$20.82	$20.80	$20.80
Purchase #3	$186.69	3.602%	$193.4146	$193.41	$193.40	$193.40
Purchase #4	$150.85	13.589%	$171.349	$171.35	$171.35	$171.30
Purchase #5	$154.71	11.758%	$172.9008	$172.90	$172.90	$172.90
Purchase #6	$74.46	5.298%	$78.4049	$78.40	$78.40	$78.40
Purchase #7	$150.26	6.438%	$159.9337	$159.93	$159.95	$159.90
7 purchase totals =	$770.94		$836.6412	$836.63	$836.60	$836.50