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	$136.59	5.858%	$144.5914	$144.59	$144.60	$144.60
Purchase #2	$41.91	5.220%	$44.0977	$44.10	$44.10	$44.10
Purchase #3	$105.95	11.612%	$118.2529	$118.25	$118.25	$118.30
Purchase #4	$82.68	8.785%	$89.9434	$89.94	$89.95	$89.90
Purchase #5	$20.75	12.364%	$23.3155	$23.32	$23.30	$23.30
Purchase #6	$198.69	9.368%	$217.3033	$217.30	$217.30	$217.30
Purchase #7	$22.74	13.490%	$25.8076	$25.81	$25.80	$25.80
7 purchase totals =	$609.31		$663.3118	$663.31	$663.30	$663.30