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	$36.99	6.292%	$39.3174	$39.32	$39.30	$39.30
Purchase #2	$205.70	3.621%	$213.1484	$213.15	$213.15	$213.10
Purchase #3	$181.39	9.856%	$199.2678	$199.27	$199.25	$199.30
Purchase #4	$119.32	12.343%	$134.0477	$134.05	$134.05	$134.00
Purchase #5	$84.88	5.155%	$89.2556	$89.26	$89.25	$89.30
Purchase #6	$117.45	11.671%	$131.1576	$131.16	$131.15	$131.20
Purchase #7	$140.42	11.365%	$156.3787	$156.38	$156.40	$156.40
7 purchase totals =	$886.15		$962.5732	$962.59	$962.55	$962.60