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	$132.58	6.710%	$141.4761	$141.48	$141.50	$141.50
Purchase #2	$152.63	9.254%	$166.7544	$166.75	$166.75	$166.80
Purchase #3	$125.57	11.353%	$139.826	$139.83	$139.85	$139.80
Purchase #4	$193.29	13.599%	$219.5755	$219.58	$219.60	$219.60
Purchase #5	$131.66	4.626%	$137.7506	$137.75	$137.75	$137.80
Purchase #6	$36.72	4.526%	$38.3819	$38.38	$38.40	$38.40
Purchase #7	$231.76	9.374%	$253.4852	$253.49	$253.50	$253.50
7 purchase totals =	$1,004.21		$1,097.2497	$1,097.26	$1,097.35	$1,097.40