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	$76.59	3.583%	$79.3342	$79.33	$79.35	$79.30
Purchase #2	$209.57	8.532%	$227.4505	$227.45	$227.45	$227.50
Purchase #3	$204.94	6.454%	$218.1668	$218.17	$218.15	$218.20
Purchase #4	$94.70	10.233%	$104.3907	$104.39	$104.40	$104.40
Purchase #5	$85.58	4.133%	$89.117	$89.12	$89.10	$89.10
Purchase #6	$61.88	7.102%	$66.2747	$66.27	$66.25	$66.30
Purchase #7	$186.73	13.740%	$212.3867	$212.39	$212.40	$212.40
7 purchase totals =	$919.99		$997.1206	$997.12	$997.10	$997.20