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	$15.30	10.649%	$16.9293	$16.93	$16.95	$16.90
Purchase #2	$63.71	13.769%	$72.4822	$72.48	$72.50	$72.50
Purchase #3	$80.52	12.767%	$90.8	$90.80	$90.80	$90.80
Purchase #4	$56.26	9.700%	$61.7172	$61.72	$61.70	$61.70
Purchase #5	$139.49	10.749%	$154.4838	$154.48	$154.50	$154.50
Purchase #6	$6.98	7.204%	$7.4828	$7.48	$7.50	$7.50
Purchase #7	$85.49	4.675%	$89.4867	$89.49	$89.50	$89.50
7 purchase totals =	$447.75		$493.3820	$493.38	$493.45	$493.40