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	$40.84	4.220%	$42.5634	$42.56	$42.55	$42.60
Purchase #2	$186.28	5.397%	$196.3335	$196.33	$196.35	$196.30
Purchase #3	$160.59	12.342%	$180.41	$180.41	$180.40	$180.40
Purchase #4	$119.48	10.261%	$131.7398	$131.74	$131.75	$131.70
Purchase #5	$84.86	12.493%	$95.4616	$95.46	$95.45	$95.50
Purchase #6	$224.62	13.856%	$255.7433	$255.74	$255.75	$255.70
Purchase #7	$61.50	10.603%	$68.0208	$68.02	$68.00	$68.00
7 purchase totals =	$878.17		$970.2724	$970.26	$970.25	$970.20