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	$154.91	11.116%	$172.1298	$172.13	$172.15	$172.10
Purchase #2	$142.31	12.386%	$159.9365	$159.94	$159.95	$159.90
Purchase #3	$75.54	4.778%	$79.1493	$79.15	$79.15	$79.10
Purchase #4	$39.65	9.193%	$43.295	$43.30	$43.30	$43.30
Purchase #5	$55.55	7.842%	$59.9062	$59.91	$59.90	$59.90
Purchase #6	$131.61	12.718%	$148.3482	$148.35	$148.35	$148.30
Purchase #7	$22.34	13.541%	$25.3651	$25.37	$25.35	$25.40
7 purchase totals =	$621.91		$688.1301	$688.15	$688.15	$688.00