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	$136.62	6.739%	$145.8268	$145.83	$145.85	$145.80
Purchase #2	$138.93	9.319%	$151.8769	$151.88	$151.90	$151.90
Purchase #3	$34.88	9.802%	$38.2989	$38.30	$38.30	$38.30
Purchase #4	$177.59	4.383%	$185.3738	$185.37	$185.35	$185.40
Purchase #5	$248.66	13.740%	$282.8259	$282.83	$282.85	$282.80
Purchase #6	$185.87	7.432%	$199.6839	$199.68	$199.70	$199.70
Purchase #7	$55.49	10.651%	$61.4002	$61.40	$61.40	$61.40
7 purchase totals =	$978.04		$1,065.2864	$1,065.29	$1,065.35	$1,065.30