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	$197.45	12.604%	$222.3366	$222.34	$222.35	$222.30
Purchase #2	$22.51	6.196%	$23.9047	$23.90	$23.90	$23.90
Purchase #3	$86.79	6.558%	$92.4817	$92.48	$92.50	$92.50
Purchase #4	$42.45	3.837%	$44.0788	$44.08	$44.10	$44.10
Purchase #5	$100.92	4.385%	$105.3453	$105.35	$105.35	$105.30
Purchase #6	$243.64	9.481%	$266.7395	$266.74	$266.75	$266.70
Purchase #7	$82.34	3.292%	$85.0506	$85.05	$85.05	$85.10
7 purchase totals =	$776.10		$839.9372	$839.94	$840.00	$839.90