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	$31.56	12.756%	$35.5858	$35.59	$35.60	$35.60
Purchase #2	$143.64	3.243%	$148.2982	$148.30	$148.30	$148.30
Purchase #3	$143.82	5.425%	$151.6222	$151.62	$151.60	$151.60
Purchase #4	$61.42	10.645%	$67.9582	$67.96	$67.95	$68.00
Purchase #5	$83.79	6.260%	$89.0353	$89.04	$89.05	$89.00
Purchase #6	$124.31	4.630%	$130.0656	$130.07	$130.05	$130.10
Purchase #7	$49.47	13.265%	$56.0322	$56.03	$56.05	$56.00
7 purchase totals =	$638.01		$678.5975	$678.61	$678.60	$678.60