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	$165.64	12.559%	$186.4427	$186.44	$186.45	$186.40
Purchase #2	$40.51	4.338%	$42.2673	$42.27	$42.25	$42.30
Purchase #3	$132.79	10.470%	$146.6931	$146.69	$146.70	$146.70
Purchase #4	$188.25	13.152%	$213.0086	$213.01	$213.00	$213.00
Purchase #5	$105.29	13.111%	$119.0946	$119.09	$119.10	$119.10
Purchase #6	$81.42	5.752%	$86.1033	$86.10	$86.10	$86.10
Purchase #7	$172.46	5.129%	$181.3055	$181.31	$181.30	$181.30
7 purchase totals =	$886.36		$974.9151	$974.91	$974.90	$974.90