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	$83.52	8.219%	$90.3845	$90.38	$90.40	$90.40
Purchase #2	$239.43	13.141%	$270.8935	$270.89	$270.90	$270.90
Purchase #3	$62.82	4.702%	$65.7738	$65.77	$65.75	$65.80
Purchase #4	$79.25	5.716%	$83.7799	$83.78	$83.80	$83.80
Purchase #5	$171.32	5.727%	$181.1315	$181.13	$181.15	$181.10
Purchase #6	$105.30	13.714%	$119.7408	$119.74	$119.75	$119.70
Purchase #7	$64.93	9.438%	$71.0581	$71.06	$71.05	$71.10
7 purchase totals =	$806.57		$882.7621	$882.75	$882.80	$882.80