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	$80.59	11.307%	$89.7023	$89.70	$89.70	$89.70
Purchase #2	$97.35	4.532%	$101.7619	$101.76	$101.75	$101.80
Purchase #3	$198.40	10.849%	$219.9244	$219.92	$219.90	$219.90
Purchase #4	$51.47	6.573%	$54.8531	$54.85	$54.85	$54.90
Purchase #5	$95.26	3.454%	$98.5503	$98.55	$98.55	$98.60
Purchase #6	$81.25	6.843%	$86.8099	$86.81	$86.80	$86.80
Purchase #7	$134.50	6.256%	$142.9143	$142.91	$142.90	$142.90
7 purchase totals =	$738.82		$794.5162	$794.50	$794.45	$794.60