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	$79.64	13.627%	$90.4925	$90.49	$90.50	$90.50
Purchase #2	$110.88	9.813%	$121.7607	$121.76	$121.75	$121.80
Purchase #3	$90.82	10.578%	$100.4269	$100.43	$100.45	$100.40
Purchase #4	$172.45	13.155%	$195.1358	$195.14	$195.15	$195.10
Purchase #5	$107.36	12.253%	$120.5148	$120.51	$120.50	$120.50
Purchase #6	$84.28	13.710%	$95.8348	$95.83	$95.85	$95.80
Purchase #7	$160.89	8.639%	$174.7893	$174.79	$174.80	$174.80
7 purchase totals =	$806.32		$898.9548	$898.95	$899.00	$898.90