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	$15.82	7.376%	$16.9869	$16.99	$17.00	$17.00
Purchase #2	$132.30	5.740%	$139.894	$139.89	$139.90	$139.90
Purchase #3	$84.27	7.442%	$90.5414	$90.54	$90.55	$90.50
Purchase #4	$81.59	11.306%	$90.8146	$90.81	$90.80	$90.80
Purchase #5	$98.42	4.570%	$102.9178	$102.92	$102.90	$102.90
Purchase #6	$13.69	10.684%	$15.1526	$15.15	$15.15	$15.20
Purchase #7	$240.60	4.225%	$250.7654	$250.77	$250.75	$250.80
7 purchase totals =	$666.69		$707.0727	$707.07	$707.05	$707.10