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	$229.51	9.753%	$251.8941	$251.89	$251.90	$251.90
Purchase #2	$65.45	9.103%	$71.4079	$71.41	$71.40	$71.40
Purchase #3	$117.85	11.512%	$131.4169	$131.42	$131.40	$131.40
Purchase #4	$213.37	13.157%	$241.4431	$241.44	$241.45	$241.40
Purchase #5	$97.43	12.113%	$109.2317	$109.23	$109.25	$109.20
Purchase #6	$134.48	10.669%	$148.8277	$148.83	$148.85	$148.80
Purchase #7	$38.99	5.166%	$41.0042	$41.00	$41.00	$41.00
7 purchase totals =	$897.08		$995.2256	$995.22	$995.25	$995.10