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	$60.71	9.649%	$66.5679	$66.57	$66.55	$66.60
Purchase #2	$33.59	5.165%	$35.3249	$35.32	$35.30	$35.30
Purchase #3	$208.25	8.165%	$225.2536	$225.25	$225.25	$225.30
Purchase #4	$47.66	7.784%	$51.3699	$51.37	$51.35	$51.40
Purchase #5	$36.42	7.556%	$39.1719	$39.17	$39.15	$39.20
Purchase #6	$97.98	12.753%	$110.4754	$110.48	$110.50	$110.50
Purchase #7	$37.97	11.650%	$42.3935	$42.39	$42.40	$42.40
7 purchase totals =	$522.58		$570.5571	$570.55	$570.50	$570.70