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	$247.74	6.810%	$264.6111	$264.61	$264.60	$264.60
Purchase #2	$11.34	8.645%	$12.3203	$12.32	$12.30	$12.30
Purchase #3	$52.87	3.678%	$54.8146	$54.81	$54.80	$54.80
Purchase #4	$182.61	3.317%	$188.6672	$188.67	$188.65	$188.70
Purchase #5	$90.70	10.687%	$100.3931	$100.39	$100.40	$100.40
Purchase #6	$103.72	3.237%	$107.0774	$107.08	$107.10	$107.10
Purchase #7	$32.30	9.258%	$35.2903	$35.29	$35.30	$35.30
7 purchase totals =	$721.28		$763.1740	$763.17	$763.15	$763.20