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	$28.30	6.322%	$30.0891	$30.09	$30.10	$30.10
Purchase #2	$141.87	7.203%	$152.0889	$152.09	$152.10	$152.10
Purchase #3	$40.90	5.206%	$43.0293	$43.03	$43.05	$43.00
Purchase #4	$81.80	12.726%	$92.2099	$92.21	$92.20	$92.20
Purchase #5	$63.47	13.646%	$72.1311	$72.13	$72.15	$72.10
Purchase #6	$214.79	8.736%	$233.5541	$233.55	$233.55	$233.60
Purchase #7	$55.46	10.654%	$61.3687	$61.37	$61.35	$61.40
7 purchase totals =	$626.59		$684.4711	$684.47	$684.50	$684.50