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	$13.94	11.344%	$15.5214	$15.52	$15.50	$15.50
Purchase #2	$94.60	5.522%	$99.8238	$99.82	$99.80	$99.80
Purchase #3	$85.66	8.520%	$92.9582	$92.96	$92.95	$93.00
Purchase #4	$106.37	6.655%	$113.4489	$113.45	$113.45	$113.40
Purchase #5	$99.35	4.204%	$103.5267	$103.53	$103.55	$103.50
Purchase #6	$124.68	5.452%	$131.4776	$131.48	$131.50	$131.50
Purchase #7	$15.44	7.447%	$16.5898	$16.59	$16.60	$16.60
7 purchase totals =	$540.04		$573.3464	$573.35	$573.35	$573.30