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	$100.53	6.689%	$107.2545	$107.25	$107.25	$107.30
Purchase #2	$248.67	6.816%	$265.6193	$265.62	$265.60	$265.60
Purchase #3	$43.27	10.679%	$47.8908	$47.89	$47.90	$47.90
Purchase #4	$248.31	12.559%	$279.4953	$279.50	$279.50	$279.50
Purchase #5	$150.37	13.311%	$170.3858	$170.39	$170.40	$170.40
Purchase #6	$173.27	11.593%	$193.3572	$193.36	$193.35	$193.40
Purchase #7	$112.78	13.308%	$127.7888	$127.79	$127.80	$127.80
7 purchase totals =	$1,077.20		$1,191.7917	$1,191.80	$1,191.80	$1,191.90