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	$90.36	6.152%	$95.9189	$95.92	$95.90	$95.90
Purchase #2	$192.80	7.298%	$206.8705	$206.87	$206.85	$206.90
Purchase #3	$155.89	13.841%	$177.4667	$177.47	$177.45	$177.50
Purchase #4	$107.60	3.593%	$111.4661	$111.47	$111.45	$111.50
Purchase #5	$155.46	8.858%	$169.2306	$169.23	$169.25	$169.20
Purchase #6	$106.42	7.780%	$114.6995	$114.70	$114.70	$114.70
Purchase #7	$39.33	6.422%	$41.8558	$41.86	$41.85	$41.90
7 purchase totals =	$847.86		$917.5081	$917.52	$917.45	$917.60