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	$139.90	13.456%	$158.7249	$158.72	$158.70	$158.70
Purchase #2	$67.98	13.457%	$77.1281	$77.13	$77.15	$77.10
Purchase #3	$164.63	8.752%	$179.0384	$179.04	$179.05	$179.00
Purchase #4	$56.38	9.166%	$61.5478	$61.55	$61.55	$61.50
Purchase #5	$188.60	12.540%	$212.2504	$212.25	$212.25	$212.30
Purchase #6	$215.78	5.794%	$228.2823	$228.28	$228.30	$228.30
Purchase #7	$135.79	11.470%	$151.3651	$151.37	$151.35	$151.40
7 purchase totals =	$969.06		$1,068.3370	$1,068.34	$1,068.35	$1,068.30