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	$59.60	11.354%	$66.367	$66.37	$66.35	$66.40
Purchase #2	$225.97	5.711%	$238.8751	$238.88	$238.90	$238.90
Purchase #3	$130.55	7.118%	$139.8425	$139.84	$139.85	$139.80
Purchase #4	$129.59	12.834%	$146.2216	$146.22	$146.20	$146.20
Purchase #5	$173.94	6.658%	$185.5209	$185.52	$185.50	$185.50
Purchase #6	$11.45	7.647%	$12.3256	$12.33	$12.35	$12.30
Purchase #7	$18.40	8.527%	$19.969	$19.97	$19.95	$20.00
7 purchase totals =	$749.50		$809.1217	$809.13	$809.10	$809.10