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	$12.92	4.495%	$13.5008	$13.50	$13.50	$13.50
Purchase #2	$114.69	13.769%	$130.4817	$130.48	$130.50	$130.50
Purchase #3	$72.97	13.819%	$83.0537	$83.05	$83.05	$83.10
Purchase #4	$142.35	6.244%	$151.2383	$151.24	$151.25	$151.20
Purchase #5	$16.68	11.779%	$18.6447	$18.64	$18.65	$18.60
Purchase #6	$101.93	7.761%	$109.8408	$109.84	$109.85	$109.80
Purchase #7	$59.55	6.438%	$63.3838	$63.38	$63.40	$63.40
7 purchase totals =	$521.09		$570.1438	$570.13	$570.20	$570.10