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	$93.69	7.331%	$100.5584	$100.56	$100.55	$100.60
Purchase #2	$42.45	10.331%	$46.8355	$46.84	$46.85	$46.80
Purchase #3	$139.71	11.522%	$155.8074	$155.81	$155.80	$155.80
Purchase #4	$41.54	12.102%	$46.5672	$46.57	$46.55	$46.60
Purchase #5	$140.32	8.504%	$152.2528	$152.25	$152.25	$152.30
Purchase #6	$239.27	13.519%	$271.6169	$271.62	$271.60	$271.60
Purchase #7	$224.60	9.293%	$245.4721	$245.47	$245.45	$245.50
7 purchase totals =	$921.58		$1,019.1103	$1,019.12	$1,019.05	$1,019.20