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	$117.54	12.624%	$132.3782	$132.38	$132.40	$132.40
Purchase #2	$63.26	5.582%	$66.7912	$66.79	$66.80	$66.80
Purchase #3	$12.25	9.215%	$13.3788	$13.38	$13.40	$13.40
Purchase #4	$120.57	10.566%	$133.3094	$133.31	$133.30	$133.30
Purchase #5	$228.72	11.375%	$254.7369	$254.74	$254.75	$254.70
Purchase #6	$117.45	12.315%	$131.914	$131.91	$131.90	$131.90
Purchase #7	$98.78	12.792%	$111.4159	$111.42	$111.40	$111.40
7 purchase totals =	$758.57		$843.9244	$843.93	$843.95	$843.90