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	$119.34	3.558%	$123.5861	$123.59	$123.60	$123.60
Purchase #2	$229.64	10.107%	$252.8497	$252.85	$252.85	$252.80
Purchase #3	$63.94	13.524%	$72.5872	$72.59	$72.60	$72.60
Purchase #4	$38.53	8.416%	$41.7727	$41.77	$41.75	$41.80
Purchase #5	$120.79	10.489%	$133.4597	$133.46	$133.45	$133.50
Purchase #6	$40.42	8.128%	$43.7053	$43.71	$43.70	$43.70
Purchase #7	$152.54	8.760%	$165.9025	$165.90	$165.90	$165.90
7 purchase totals =	$765.20		$833.8632	$833.87	$833.85	$833.90