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	$28.90	7.806%	$31.1559	$31.16	$31.15	$31.20
Purchase #2	$82.56	13.305%	$93.5446	$93.54	$93.55	$93.50
Purchase #3	$133.88	5.668%	$141.4683	$141.47	$141.45	$141.50
Purchase #4	$115.52	7.202%	$123.8398	$123.84	$123.85	$123.80
Purchase #5	$30.49	6.283%	$32.4057	$32.41	$32.40	$32.40
Purchase #6	$223.45	12.431%	$251.2271	$251.23	$251.25	$251.20
Purchase #7	$108.49	3.466%	$112.2503	$112.25	$112.25	$112.30
7 purchase totals =	$723.29		$785.8917	$785.90	$785.90	$785.90