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	$18.85	9.290%	$20.6012	$20.60	$20.60	$20.60
Purchase #2	$112.95	13.670%	$128.3903	$128.39	$128.40	$128.40
Purchase #3	$60.99	11.341%	$67.9069	$67.91	$67.90	$67.90
Purchase #4	$234.33	11.523%	$261.3318	$261.33	$261.35	$261.30
Purchase #5	$40.32	4.480%	$42.1263	$42.13	$42.15	$42.10
Purchase #6	$140.26	5.161%	$147.4988	$147.50	$147.50	$147.50
Purchase #7	$55.52	3.727%	$57.5892	$57.59	$57.60	$57.60
7 purchase totals =	$663.22		$725.4445	$725.45	$725.50	$725.40