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	$60.84	12.319%	$68.3349	$68.33	$68.35	$68.30
Purchase #2	$40.81	3.535%	$42.2526	$42.25	$42.25	$42.30
Purchase #3	$63.91	13.447%	$72.504	$72.50	$72.50	$72.50
Purchase #4	$156.80	12.534%	$176.4533	$176.45	$176.45	$176.50
Purchase #5	$53.51	11.512%	$59.6701	$59.67	$59.65	$59.70
Purchase #6	$135.76	5.331%	$142.9974	$143.00	$143.00	$143.00
Purchase #7	$112.92	3.128%	$116.4521	$116.45	$116.45	$116.50
7 purchase totals =	$624.55		$678.6644	$678.65	$678.65	$678.80