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	$82.70	8.356%	$89.6104	$89.61	$89.60	$89.60
Purchase #2	$101.37	9.637%	$111.139	$111.14	$111.15	$111.10
Purchase #3	$113.51	4.720%	$118.8677	$118.87	$118.85	$118.90
Purchase #4	$41.95	9.615%	$45.9835	$45.98	$46.00	$46.00
Purchase #5	$83.81	13.408%	$95.0472	$95.05	$95.05	$95.00
Purchase #6	$85.70	13.669%	$97.4143	$97.41	$97.40	$97.40
Purchase #7	$56.91	9.594%	$62.3699	$62.37	$62.35	$62.40
7 purchase totals =	$565.95		$620.4320	$620.43	$620.40	$620.40