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	$160.83	5.191%	$169.1787	$169.18	$169.20	$169.20
Purchase #2	$31.40	10.776%	$34.7837	$34.78	$34.80	$34.80
Purchase #3	$74.25	12.440%	$83.4867	$83.49	$83.50	$83.50
Purchase #4	$241.72	11.243%	$268.8966	$268.90	$268.90	$268.90
Purchase #5	$134.40	7.434%	$144.3913	$144.39	$144.40	$144.40
Purchase #6	$192.32	12.528%	$216.4138	$216.41	$216.40	$216.40
Purchase #7	$39.35	7.215%	$42.1891	$42.19	$42.20	$42.20
7 purchase totals =	$874.27		$959.3399	$959.34	$959.40	$959.40