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	$174.72	3.108%	$180.1503	$180.15	$180.15	$180.20
Purchase #2	$126.57	4.205%	$131.8923	$131.89	$131.90	$131.90
Purchase #3	$240.34	11.437%	$267.8277	$267.83	$267.85	$267.80
Purchase #4	$92.87	7.700%	$100.021	$100.02	$100.00	$100.00
Purchase #5	$154.66	10.873%	$171.4762	$171.48	$171.50	$171.50
Purchase #6	$141.45	9.264%	$154.5539	$154.55	$154.55	$154.60
Purchase #7	$154.87	12.779%	$174.6608	$174.66	$174.65	$174.70
7 purchase totals =	$1,085.48		$1,180.5822	$1,180.58	$1,180.60	$1,180.70