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	$107.89	7.626%	$116.1177	$116.12	$116.10	$116.10
Purchase #2	$210.61	13.545%	$239.1371	$239.14	$239.15	$239.10
Purchase #3	$40.25	8.474%	$43.6608	$43.66	$43.65	$43.70
Purchase #4	$222.93	11.496%	$248.558	$248.56	$248.55	$248.60
Purchase #5	$69.79	12.611%	$78.5912	$78.59	$78.60	$78.60
Purchase #6	$250.89	8.258%	$271.6085	$271.61	$271.60	$271.60
Purchase #7	$235.43	10.280%	$259.6322	$259.63	$259.65	$259.60
7 purchase totals =	$1,137.79		$1,257.3055	$1,257.31	$1,257.30	$1,257.30