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	$90.67	10.507%	$100.1967	$100.20	$100.20	$100.20
Purchase #2	$132.86	3.279%	$137.2165	$137.22	$137.20	$137.20
Purchase #3	$57.88	3.495%	$59.9029	$59.90	$59.90	$59.90
Purchase #4	$119.78	12.418%	$134.6543	$134.65	$134.65	$134.70
Purchase #5	$148.81	12.135%	$166.8681	$166.87	$166.85	$166.90
Purchase #6	$250.62	6.387%	$266.6271	$266.63	$266.65	$266.60
Purchase #7	$96.92	7.304%	$103.999	$104.00	$104.00	$104.00
7 purchase totals =	$897.54		$969.4646	$969.47	$969.45	$969.50