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	$132.46	3.479%	$137.0683	$137.07	$137.05	$137.10
Purchase #2	$144.75	5.229%	$152.319	$152.32	$152.30	$152.30
Purchase #3	$115.97	7.413%	$124.5669	$124.57	$124.55	$124.60
Purchase #4	$133.96	8.189%	$144.93	$144.93	$144.95	$144.90
Purchase #5	$187.32	11.643%	$209.1297	$209.13	$209.15	$209.10
Purchase #6	$94.25	12.386%	$105.9238	$105.92	$105.90	$105.90
Purchase #7	$201.64	7.353%	$216.4666	$216.47	$216.45	$216.50
7 purchase totals =	$1,010.35		$1,090.4043	$1,090.41	$1,090.35	$1,090.40