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	$14.33	8.708%	$15.5779	$15.58	$15.60	$15.60
Purchase #2	$41.33	9.232%	$45.1456	$45.15	$45.15	$45.10
Purchase #3	$14.55	9.306%	$15.904	$15.90	$15.90	$15.90
Purchase #4	$160.42	12.272%	$180.1067	$180.11	$180.10	$180.10
Purchase #5	$134.80	8.764%	$146.6139	$146.61	$146.60	$146.60
Purchase #6	$134.60	5.811%	$142.4216	$142.42	$142.40	$142.40
Purchase #7	$18.32	13.173%	$20.7333	$20.73	$20.75	$20.70
7 purchase totals =	$518.35		$566.5030	$566.50	$566.50	$566.40