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	$58.64	12.570%	$66.011	$66.01	$66.00	$66.00
Purchase #2	$130.95	7.846%	$141.2243	$141.22	$141.20	$141.20
Purchase #3	$211.26	6.323%	$224.618	$224.62	$224.60	$224.60
Purchase #4	$236.76	9.224%	$258.5987	$258.60	$258.60	$258.60
Purchase #5	$174.66	12.371%	$196.2672	$196.27	$196.25	$196.30
Purchase #6	$88.79	13.407%	$100.6941	$100.69	$100.70	$100.70
Purchase #7	$143.79	13.547%	$163.2692	$163.27	$163.25	$163.30
7 purchase totals =	$1,044.85		$1,150.6825	$1,150.68	$1,150.60	$1,150.70