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	$92.87	7.808%	$100.1213	$100.12	$100.10	$100.10
Purchase #2	$166.61	5.116%	$175.1338	$175.13	$175.15	$175.10
Purchase #3	$104.89	10.215%	$115.6045	$115.60	$115.60	$115.60
Purchase #4	$232.59	8.780%	$253.0114	$253.01	$253.00	$253.00
Purchase #5	$172.89	10.314%	$190.7219	$190.72	$190.70	$190.70
Purchase #6	$41.33	13.630%	$46.9633	$46.96	$46.95	$47.00
Purchase #7	$106.68	10.763%	$118.162	$118.16	$118.15	$118.20
7 purchase totals =	$917.86		$999.7182	$999.70	$999.65	$999.70