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	$177.94	5.531%	$187.7819	$187.78	$187.80	$187.80
Purchase #2	$166.35	8.736%	$180.8823	$180.88	$180.90	$180.90
Purchase #3	$149.94	4.655%	$156.9197	$156.92	$156.90	$156.90
Purchase #4	$95.73	9.565%	$104.8866	$104.89	$104.90	$104.90
Purchase #5	$141.54	12.564%	$159.3231	$159.32	$159.30	$159.30
Purchase #6	$152.70	13.168%	$172.8075	$172.81	$172.80	$172.80
Purchase #7	$15.86	9.863%	$17.4243	$17.42	$17.40	$17.40
7 purchase totals =	$900.06		$980.0254	$980.02	$980.00	$980.00