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	$94.30	5.143%	$99.1498	$99.15	$99.15	$99.10
Purchase #2	$225.87	7.725%	$243.3185	$243.32	$243.30	$243.30
Purchase #3	$104.81	12.177%	$117.5727	$117.57	$117.55	$117.60
Purchase #4	$171.96	4.295%	$179.3457	$179.35	$179.35	$179.30
Purchase #5	$131.45	10.563%	$145.3351	$145.34	$145.35	$145.30
Purchase #6	$234.99	13.436%	$266.5633	$266.56	$266.55	$266.60
Purchase #7	$19.77	5.557%	$20.8686	$20.87	$20.85	$20.90
7 purchase totals =	$983.15		$1,072.1537	$1,072.16	$1,072.10	$1,072.10