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	$148.88	6.801%	$159.0053	$159.01	$159.00	$159.00
Purchase #2	$87.42	3.813%	$90.7533	$90.75	$90.75	$90.80
Purchase #3	$129.80	6.689%	$138.4823	$138.48	$138.50	$138.50
Purchase #4	$174.94	5.256%	$184.1348	$184.13	$184.15	$184.10
Purchase #5	$185.47	4.557%	$193.9219	$193.92	$193.90	$193.90
Purchase #6	$118.82	9.256%	$129.818	$129.82	$129.80	$129.80
Purchase #7	$99.87	13.597%	$113.4493	$113.45	$113.45	$113.40
7 purchase totals =	$945.20		$1,009.5649	$1,009.56	$1,009.55	$1,009.50