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	$132.49	11.803%	$148.1278	$148.13	$148.15	$148.10
Purchase #2	$225.46	13.125%	$255.0516	$255.05	$255.05	$255.10
Purchase #3	$233.98	8.435%	$253.7162	$253.72	$253.70	$253.70
Purchase #4	$156.42	6.221%	$166.1509	$166.15	$166.15	$166.20
Purchase #5	$132.49	11.755%	$148.0642	$148.06	$148.05	$148.10
Purchase #6	$16.90	9.507%	$18.5067	$18.51	$18.50	$18.50
Purchase #7	$137.94	13.135%	$156.0584	$156.06	$156.05	$156.10
7 purchase totals =	$1,035.68		$1,145.6758	$1,145.68	$1,145.65	$1,145.80