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	$17.93	8.361%	$19.4291	$19.43	$19.45	$19.40
Purchase #2	$85.38	10.349%	$94.216	$94.22	$94.20	$94.20
Purchase #3	$79.69	12.491%	$89.6441	$89.64	$89.65	$89.60
Purchase #4	$154.88	6.223%	$164.5182	$164.52	$164.50	$164.50
Purchase #5	$48.51	4.134%	$50.5154	$50.52	$50.50	$50.50
Purchase #6	$79.60	5.380%	$83.8825	$83.88	$83.90	$83.90
Purchase #7	$79.30	11.700%	$88.5781	$88.58	$88.60	$88.60
7 purchase totals =	$545.29		$590.7834	$590.79	$590.80	$590.70