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	$101.59	9.329%	$111.0673	$111.07	$111.05	$111.10
Purchase #2	$57.81	13.212%	$65.4479	$65.45	$65.45	$65.40
Purchase #3	$164.29	11.136%	$182.5853	$182.59	$182.60	$182.60
Purchase #4	$237.32	13.804%	$270.0797	$270.08	$270.10	$270.10
Purchase #5	$79.31	11.377%	$88.3331	$88.33	$88.35	$88.30
Purchase #6	$39.66	11.407%	$44.184	$44.18	$44.20	$44.20
Purchase #7	$131.92	4.756%	$138.1941	$138.19	$138.20	$138.20
7 purchase totals =	$811.90		$899.8914	$899.89	$899.95	$899.90