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	$32.83	6.233%	$34.8763	$34.88	$34.90	$34.90
Purchase #2	$89.44	7.399%	$96.0577	$96.06	$96.05	$96.10
Purchase #3	$199.47	4.222%	$207.8916	$207.89	$207.90	$207.90
Purchase #4	$132.89	9.504%	$145.5199	$145.52	$145.50	$145.50
Purchase #5	$61.25	9.665%	$67.1698	$67.17	$67.15	$67.20
Purchase #6	$157.29	4.627%	$164.5678	$164.57	$164.55	$164.60
Purchase #7	$203.87	3.262%	$210.5202	$210.52	$210.50	$210.50
7 purchase totals =	$877.04		$926.6033	$926.61	$926.55	$926.70