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	$238.44	8.719%	$259.2296	$259.23	$259.25	$259.20
Purchase #2	$146.26	8.679%	$158.9539	$158.95	$158.95	$159.00
Purchase #3	$16.42	9.263%	$17.941	$17.94	$17.95	$17.90
Purchase #4	$84.31	7.711%	$90.8111	$90.81	$90.80	$90.80
Purchase #5	$146.85	3.208%	$151.5609	$151.56	$151.55	$151.60
Purchase #6	$81.43	5.388%	$85.8174	$85.82	$85.80	$85.80
Purchase #7	$83.34	8.378%	$90.3222	$90.32	$90.30	$90.30
7 purchase totals =	$797.05		$854.6361	$854.63	$854.60	$854.60