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	$69.37	13.220%	$78.5407	$78.54	$78.55	$78.50
Purchase #2	$80.63	3.246%	$83.2472	$83.25	$83.25	$83.20
Purchase #3	$149.88	8.666%	$162.8686	$162.87	$162.85	$162.90
Purchase #4	$212.30	11.189%	$236.0542	$236.05	$236.05	$236.10
Purchase #5	$193.34	13.453%	$219.35	$219.35	$219.35	$219.40
Purchase #6	$106.42	4.690%	$111.4111	$111.41	$111.40	$111.40
Purchase #7	$226.87	9.371%	$248.13	$248.13	$248.15	$248.10
7 purchase totals =	$1,038.81		$1,139.6018	$1,139.60	$1,139.60	$1,139.60