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	$14.25	11.437%	$15.8798	$15.88	$15.90	$15.90
Purchase #2	$16.41	4.617%	$17.1676	$17.17	$17.15	$17.20
Purchase #3	$70.45	11.665%	$78.668	$78.67	$78.65	$78.70
Purchase #4	$117.64	7.863%	$126.89	$126.89	$126.90	$126.90
Purchase #5	$127.48	10.836%	$141.2937	$141.29	$141.30	$141.30
Purchase #6	$227.99	10.231%	$251.3157	$251.32	$251.30	$251.30
Purchase #7	$190.43	5.200%	$200.3324	$200.33	$200.35	$200.30
7 purchase totals =	$764.65		$831.5472	$831.55	$831.55	$831.60