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	$48.71	8.567%	$52.883	$52.88	$52.90	$52.90
Purchase #2	$59.50	12.310%	$66.8245	$66.82	$66.80	$66.80
Purchase #3	$15.62	11.522%	$17.4197	$17.42	$17.40	$17.40
Purchase #4	$79.44	13.306%	$90.0103	$90.01	$90.00	$90.00
Purchase #5	$34.36	9.804%	$37.7287	$37.73	$37.75	$37.70
Purchase #6	$226.28	5.799%	$239.402	$239.40	$239.40	$239.40
Purchase #7	$51.37	4.264%	$53.5604	$53.56	$53.55	$53.60
7 purchase totals =	$515.28		$557.8286	$557.82	$557.80	$557.80