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	$146.89	13.553%	$166.798	$166.80	$166.80	$166.80
Purchase #2	$136.88	7.248%	$146.8011	$146.80	$146.80	$146.80
Purchase #3	$84.59	5.238%	$89.0208	$89.02	$89.00	$89.00
Purchase #4	$89.98	12.694%	$101.4021	$101.40	$101.40	$101.40
Purchase #5	$126.44	8.455%	$137.1305	$137.13	$137.15	$137.10
Purchase #6	$160.76	5.216%	$169.1452	$169.15	$169.15	$169.10
Purchase #7	$159.53	13.279%	$180.714	$180.71	$180.70	$180.70
7 purchase totals =	$905.07		$991.0117	$991.01	$991.00	$990.90