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	$24.79	12.520%	$27.8937	$27.89	$27.90	$27.90
Purchase #2	$76.45	3.428%	$79.0707	$79.07	$79.05	$79.10
Purchase #3	$139.55	4.549%	$145.8981	$145.90	$145.90	$145.90
Purchase #4	$224.33	10.720%	$248.3782	$248.38	$248.40	$248.40
Purchase #5	$191.67	10.239%	$211.2951	$211.30	$211.30	$211.30
Purchase #6	$205.63	13.570%	$233.534	$233.53	$233.55	$233.50
Purchase #7	$190.86	7.676%	$205.5104	$205.51	$205.50	$205.50
7 purchase totals =	$1,053.28		$1,151.5802	$1,151.58	$1,151.60	$1,151.60