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	$41.60	5.436%	$43.8614	$43.86	$43.85	$43.90
Purchase #2	$199.25	13.124%	$225.3996	$225.40	$225.40	$225.40
Purchase #3	$74.77	7.356%	$80.2701	$80.27	$80.25	$80.30
Purchase #4	$42.63	4.325%	$44.4737	$44.47	$44.45	$44.50
Purchase #5	$248.41	13.439%	$281.7938	$281.79	$281.80	$281.80
Purchase #6	$35.34	3.192%	$36.4681	$36.47	$36.45	$36.50
Purchase #7	$79.98	8.150%	$86.4984	$86.50	$86.50	$86.50
7 purchase totals =	$721.98		$798.7651	$798.76	$798.70	$798.90