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	$10.68	10.780%	$11.8313	$11.83	$11.85	$11.80
Purchase #2	$233.60	11.239%	$259.8543	$259.85	$259.85	$259.90
Purchase #3	$150.41	6.766%	$160.5867	$160.59	$160.60	$160.60
Purchase #4	$148.80	11.547%	$165.9819	$165.98	$166.00	$166.00
Purchase #5	$91.73	11.438%	$102.2221	$102.22	$102.20	$102.20
Purchase #6	$71.30	10.642%	$78.8877	$78.89	$78.90	$78.90
Purchase #7	$133.94	11.724%	$149.6431	$149.64	$149.65	$149.60
7 purchase totals =	$840.46		$929.0071	$929.00	$929.05	$929.00