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	$219.79	13.219%	$248.844	$248.84	$248.85	$248.80
Purchase #2	$191.80	12.611%	$215.9879	$215.99	$216.00	$216.00
Purchase #3	$137.84	6.332%	$146.568	$146.57	$146.55	$146.60
Purchase #4	$19.58	10.474%	$21.6308	$21.63	$21.65	$21.60
Purchase #5	$85.77	4.823%	$89.9067	$89.91	$89.90	$89.90
Purchase #6	$93.70	11.625%	$104.5926	$104.59	$104.60	$104.60
Purchase #7	$148.61	5.372%	$156.5933	$156.59	$156.60	$156.60
7 purchase totals =	$897.09		$984.1233	$984.12	$984.15	$984.10