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	$242.29	11.515%	$270.1897	$270.19	$270.20	$270.20
Purchase #2	$87.52	3.801%	$90.8466	$90.85	$90.85	$90.80
Purchase #3	$181.69	3.811%	$188.6142	$188.61	$188.60	$188.60
Purchase #4	$45.36	12.840%	$51.1842	$51.18	$51.20	$51.20
Purchase #5	$80.46	3.162%	$83.0041	$83.00	$83.00	$83.00
Purchase #6	$6.92	5.667%	$7.3122	$7.31	$7.30	$7.30
Purchase #7	$250.32	8.827%	$272.4157	$272.42	$272.40	$272.40
7 purchase totals =	$894.56		$963.5667	$963.56	$963.55	$963.50