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	$96.95	11.819%	$108.4085	$108.41	$108.40	$108.40
Purchase #2	$136.83	7.315%	$146.8391	$146.84	$146.85	$146.80
Purchase #3	$169.72	9.341%	$185.5735	$185.57	$185.55	$185.60
Purchase #4	$78.45	8.589%	$85.1881	$85.19	$85.20	$85.20
Purchase #5	$31.56	10.676%	$34.9293	$34.93	$34.95	$34.90
Purchase #6	$77.72	5.273%	$81.8182	$81.82	$81.80	$81.80
Purchase #7	$150.57	5.435%	$158.7535	$158.75	$158.75	$158.80
7 purchase totals =	$741.80		$801.5102	$801.51	$801.50	$801.50