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	$106.48	11.382%	$118.5996	$118.60	$118.60	$118.60
Purchase #2	$174.44	6.197%	$185.25	$185.25	$185.25	$185.30
Purchase #3	$135.33	11.579%	$150.9999	$151.00	$151.00	$151.00
Purchase #4	$106.82	10.540%	$118.0788	$118.08	$118.10	$118.10
Purchase #5	$42.49	8.405%	$46.0613	$46.06	$46.05	$46.10
Purchase #6	$15.73	8.511%	$17.0688	$17.07	$17.05	$17.10
Purchase #7	$30.95	8.277%	$33.5117	$33.51	$33.50	$33.50
7 purchase totals =	$612.24		$669.5701	$669.57	$669.55	$669.70