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	$14.53	3.800%	$15.0821	$15.08	$15.10	$15.10
Purchase #2	$31.96	9.145%	$34.8827	$34.88	$34.90	$34.90
Purchase #3	$105.67	3.301%	$109.1582	$109.16	$109.15	$109.20
Purchase #4	$64.31	13.414%	$72.9365	$72.94	$72.95	$72.90
Purchase #5	$137.28	6.791%	$146.6027	$146.60	$146.60	$146.60
Purchase #6	$213.82	11.433%	$238.266	$238.27	$238.25	$238.30
Purchase #7	$51.57	8.226%	$55.8121	$55.81	$55.80	$55.80
7 purchase totals =	$619.14		$672.7403	$672.74	$672.75	$672.80