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	$72.72	5.438%	$76.6745	$76.67	$76.65	$76.70
Purchase #2	$142.96	8.313%	$154.8443	$154.84	$154.85	$154.80
Purchase #3	$88.51	12.861%	$99.8933	$99.89	$99.90	$99.90
Purchase #4	$65.67	3.213%	$67.78	$67.78	$67.80	$67.80
Purchase #5	$115.44	3.593%	$119.5878	$119.59	$119.60	$119.60
Purchase #6	$53.33	3.632%	$55.2669	$55.27	$55.25	$55.30
Purchase #7	$5.34	10.855%	$5.9197	$5.92	$5.90	$5.90
7 purchase totals =	$543.97		$579.9665	$579.96	$579.95	$580.00