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	$117.79	10.206%	$129.8116	$129.81	$129.80	$129.80
Purchase #2	$115.85	13.262%	$131.214	$131.21	$131.20	$131.20
Purchase #3	$105.50	11.872%	$118.025	$118.03	$118.05	$118.00
Purchase #4	$74.57	5.171%	$78.426	$78.43	$78.45	$78.40
Purchase #5	$64.60	4.714%	$67.6452	$67.65	$67.65	$67.60
Purchase #6	$170.51	9.582%	$186.8483	$186.85	$186.85	$186.80
Purchase #7	$79.91	12.203%	$89.6614	$89.66	$89.65	$89.70
7 purchase totals =	$728.73		$801.6315	$801.64	$801.65	$801.50