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	$24.66	13.711%	$28.0411	$28.04	$28.05	$28.00
Purchase #2	$83.98	12.832%	$94.7563	$94.76	$94.75	$94.80
Purchase #3	$165.94	5.208%	$174.5822	$174.58	$174.60	$174.60
Purchase #4	$184.61	8.270%	$199.8772	$199.88	$199.90	$199.90
Purchase #5	$68.42	5.848%	$72.4212	$72.42	$72.40	$72.40
Purchase #6	$72.33	11.465%	$80.6226	$80.62	$80.60	$80.60
Purchase #7	$196.42	10.737%	$217.5096	$217.51	$217.50	$217.50
7 purchase totals =	$796.36		$867.8102	$867.81	$867.80	$867.80