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	$129.78	12.418%	$145.8961	$145.90	$145.90	$145.90
Purchase #2	$39.92	6.706%	$42.597	$42.60	$42.60	$42.60
Purchase #3	$247.88	11.565%	$276.5473	$276.55	$276.55	$276.50
Purchase #4	$129.89	5.763%	$137.3756	$137.38	$137.40	$137.40
Purchase #5	$167.43	8.728%	$182.0433	$182.04	$182.05	$182.00
Purchase #6	$53.70	3.352%	$55.5	$55.50	$55.50	$55.50
Purchase #7	$59.35	10.140%	$65.3681	$65.37	$65.35	$65.40
7 purchase totals =	$827.95		$905.3274	$905.34	$905.35	$905.30