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	$78.28	8.796%	$85.1655	$85.17	$85.15	$85.20
Purchase #2	$12.50	5.196%	$13.1495	$13.15	$13.15	$13.10
Purchase #3	$126.94	13.772%	$144.4222	$144.42	$144.40	$144.40
Purchase #4	$65.74	11.653%	$73.4007	$73.40	$73.40	$73.40
Purchase #5	$117.49	9.488%	$128.6375	$128.64	$128.65	$128.60
Purchase #6	$162.64	9.134%	$177.4955	$177.50	$177.50	$177.50
Purchase #7	$136.89	12.688%	$154.2586	$154.26	$154.25	$154.30
7 purchase totals =	$700.48		$776.5295	$776.54	$776.50	$776.50