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	$162.64	3.215%	$167.8689	$167.87	$167.85	$167.90
Purchase #2	$97.30	6.654%	$103.7743	$103.77	$103.75	$103.80
Purchase #3	$166.51	13.761%	$189.4234	$189.42	$189.40	$189.40
Purchase #4	$184.57	7.821%	$199.0052	$199.01	$199.00	$199.00
Purchase #5	$49.57	4.561%	$51.8309	$51.83	$51.85	$51.80
Purchase #6	$70.93	12.797%	$80.0069	$80.01	$80.00	$80.00
Purchase #7	$172.92	13.647%	$196.5184	$196.52	$196.50	$196.50
7 purchase totals =	$904.44		$988.4280	$988.43	$988.35	$988.40