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	$42.45	7.150%	$45.4852	$45.49	$45.50	$45.50
Purchase #2	$32.99	9.856%	$36.2415	$36.24	$36.25	$36.20
Purchase #3	$132.72	11.187%	$147.5674	$147.57	$147.55	$147.60
Purchase #4	$86.96	3.835%	$90.2949	$90.29	$90.30	$90.30
Purchase #5	$30.49	12.185%	$34.2052	$34.21	$34.20	$34.20
Purchase #6	$195.52	7.474%	$210.1332	$210.13	$210.15	$210.10
Purchase #7	$36.64	10.644%	$40.54	$40.54	$40.55	$40.50
7 purchase totals =	$557.77		$604.4674	$604.47	$604.50	$604.40