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	$117.42	11.689%	$131.1452	$131.15	$131.15	$131.10
Purchase #2	$135.42	5.324%	$142.6298	$142.63	$142.65	$142.60
Purchase #3	$217.87	10.805%	$241.4109	$241.41	$241.40	$241.40
Purchase #4	$36.90	8.451%	$40.0184	$40.02	$40.00	$40.00
Purchase #5	$150.95	9.521%	$165.3219	$165.32	$165.30	$165.30
Purchase #6	$145.93	4.713%	$152.8077	$152.81	$152.80	$152.80
Purchase #7	$245.41	12.269%	$275.5194	$275.52	$275.50	$275.50
7 purchase totals =	$1,049.90		$1,148.8533	$1,148.86	$1,148.80	$1,148.70