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	$40.98	4.748%	$42.9257	$42.93	$42.95	$42.90
Purchase #2	$35.30	5.584%	$37.2712	$37.27	$37.25	$37.30
Purchase #3	$116.50	6.103%	$123.61	$123.61	$123.60	$123.60
Purchase #4	$26.80	7.337%	$28.7663	$28.77	$28.75	$28.80
Purchase #5	$168.64	13.244%	$190.9747	$190.97	$190.95	$191.00
Purchase #6	$15.37	5.781%	$16.2585	$16.26	$16.25	$16.30
Purchase #7	$194.85	6.789%	$208.0784	$208.08	$208.10	$208.10
7 purchase totals =	$598.44		$647.8848	$647.89	$647.85	$648.00