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	$59.54	12.851%	$67.1915	$67.19	$67.20	$67.20
Purchase #2	$142.57	9.493%	$156.1042	$156.10	$156.10	$156.10
Purchase #3	$160.98	12.822%	$181.6209	$181.62	$181.60	$181.60
Purchase #4	$39.43	8.512%	$42.7863	$42.79	$42.80	$42.80
Purchase #5	$104.87	6.226%	$111.3992	$111.40	$111.40	$111.40
Purchase #6	$55.97	13.470%	$63.5092	$63.51	$63.50	$63.50
Purchase #7	$96.80	9.331%	$105.8324	$105.83	$105.85	$105.80
7 purchase totals =	$660.16		$728.4437	$728.44	$728.45	$728.40