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	$157.38	6.357%	$167.3846	$167.38	$167.40	$167.40
Purchase #2	$112.42	8.324%	$121.7778	$121.78	$121.80	$121.80
Purchase #3	$79.83	3.612%	$82.7135	$82.71	$82.70	$82.70
Purchase #4	$117.38	10.595%	$129.8164	$129.82	$129.80	$129.80
Purchase #5	$50.69	9.122%	$55.3139	$55.31	$55.30	$55.30
Purchase #6	$87.48	13.382%	$99.1866	$99.19	$99.20	$99.20
Purchase #7	$24.88	13.856%	$28.3274	$28.33	$28.35	$28.30
7 purchase totals =	$630.06		$684.5202	$684.52	$684.55	$684.50