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	$104.60	10.228%	$115.2985	$115.30	$115.30	$115.30
Purchase #2	$158.64	12.332%	$178.2035	$178.20	$178.20	$178.20
Purchase #3	$89.78	12.115%	$100.6568	$100.66	$100.65	$100.70
Purchase #4	$27.32	4.484%	$28.545	$28.55	$28.55	$28.50
Purchase #5	$157.33	9.685%	$172.5674	$172.57	$172.55	$172.60
Purchase #6	$50.95	7.829%	$54.9389	$54.94	$54.95	$54.90
Purchase #7	$57.35	3.872%	$59.5706	$59.57	$59.55	$59.60
7 purchase totals =	$645.97		$709.7807	$709.79	$709.75	$709.80