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	$104.25	12.473%	$117.2531	$117.25	$117.25	$117.30
Purchase #2	$19.92	11.269%	$22.1648	$22.16	$22.15	$22.20
Purchase #3	$219.34	7.308%	$235.3694	$235.37	$235.35	$235.40
Purchase #4	$124.85	9.644%	$136.8905	$136.89	$136.90	$136.90
Purchase #5	$53.79	10.465%	$59.4191	$59.42	$59.40	$59.40
Purchase #6	$244.52	7.411%	$262.6414	$262.64	$262.65	$262.60
Purchase #7	$53.36	5.772%	$56.4399	$56.44	$56.45	$56.40
7 purchase totals =	$820.03		$890.1782	$890.17	$890.15	$890.20