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	$116.44	6.404%	$123.8968	$123.90	$123.90	$123.90
Purchase #2	$90.53	9.219%	$98.876	$98.88	$98.90	$98.90
Purchase #3	$212.64	10.579%	$235.1352	$235.14	$235.15	$235.10
Purchase #4	$188.85	11.465%	$210.5017	$210.50	$210.50	$210.50
Purchase #5	$172.89	5.145%	$181.7852	$181.79	$181.80	$181.80
Purchase #6	$239.99	6.725%	$256.1293	$256.13	$256.15	$256.10
Purchase #7	$28.62	11.552%	$31.9262	$31.93	$31.95	$31.90
7 purchase totals =	$1,049.96		$1,138.2504	$1,138.27	$1,138.35	$1,138.20