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	$52.83	13.381%	$59.8992	$59.90	$59.90	$59.90
Purchase #2	$129.98	5.794%	$137.511	$137.51	$137.50	$137.50
Purchase #3	$129.85	9.535%	$142.2312	$142.23	$142.25	$142.20
Purchase #4	$104.61	8.182%	$113.1692	$113.17	$113.15	$113.20
Purchase #5	$221.25	12.516%	$248.9417	$248.94	$248.95	$248.90
Purchase #6	$175.89	7.144%	$188.4556	$188.46	$188.45	$188.50
Purchase #7	$51.45	9.545%	$56.3609	$56.36	$56.35	$56.40
7 purchase totals =	$865.86		$946.5688	$946.57	$946.55	$946.60