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	$36.70	10.356%	$40.5007	$40.50	$40.50	$40.50
Purchase #2	$222.88	3.119%	$229.8316	$229.83	$229.85	$229.80
Purchase #3	$153.89	10.204%	$169.5929	$169.59	$169.60	$169.60
Purchase #4	$240.31	13.111%	$271.817	$271.82	$271.80	$271.80
Purchase #5	$103.70	9.821%	$113.8844	$113.88	$113.90	$113.90
Purchase #6	$37.92	13.527%	$43.0494	$43.05	$43.05	$43.00
Purchase #7	$191.78	13.217%	$217.1276	$217.13	$217.15	$217.10
7 purchase totals =	$987.18		$1,085.8036	$1,085.80	$1,085.85	$1,085.70