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	$171.93	5.759%	$181.8314	$181.83	$181.85	$181.80
Purchase #2	$114.85	3.553%	$118.9306	$118.93	$118.95	$118.90
Purchase #3	$73.63	12.208%	$82.6188	$82.62	$82.60	$82.60
Purchase #4	$74.65	8.299%	$80.8452	$80.85	$80.85	$80.80
Purchase #5	$21.46	11.207%	$23.865	$23.87	$23.85	$23.90
Purchase #6	$53.88	9.574%	$59.0385	$59.04	$59.05	$59.00
Purchase #7	$19.74	5.496%	$20.8249	$20.82	$20.80	$20.80
7 purchase totals =	$530.14		$567.9544	$567.96	$567.95	$567.80