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	$127.55	9.516%	$139.6877	$139.69	$139.70	$139.70
Purchase #2	$111.90	10.252%	$123.372	$123.37	$123.35	$123.40
Purchase #3	$147.83	11.169%	$164.3411	$164.34	$164.35	$164.30
Purchase #4	$123.46	7.625%	$132.8738	$132.87	$132.85	$132.90
Purchase #5	$188.40	12.645%	$212.2232	$212.22	$212.20	$212.20
Purchase #6	$30.66	12.285%	$34.4266	$34.43	$34.45	$34.40
Purchase #7	$7.71	3.242%	$7.96	$7.96	$7.95	$8.00
7 purchase totals =	$737.51		$814.8844	$814.88	$814.85	$814.90