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	$43.59	5.119%	$45.8214	$45.82	$45.80	$45.80
Purchase #2	$186.61	12.322%	$209.6041	$209.60	$209.60	$209.60
Purchase #3	$81.35	10.329%	$89.7526	$89.75	$89.75	$89.80
Purchase #4	$162.58	11.282%	$180.9223	$180.92	$180.90	$180.90
Purchase #5	$139.37	13.204%	$157.7724	$157.77	$157.75	$157.80
Purchase #6	$27.53	10.776%	$30.4966	$30.50	$30.50	$30.50
Purchase #7	$22.59	5.698%	$23.8772	$23.88	$23.90	$23.90
7 purchase totals =	$663.62		$738.2466	$738.24	$738.20	$738.30