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	$93.69	10.585%	$103.6071	$103.61	$103.60	$103.60
Purchase #2	$82.62	9.755%	$90.6796	$90.68	$90.70	$90.70
Purchase #3	$97.54	9.247%	$106.5595	$106.56	$106.55	$106.60
Purchase #4	$63.69	5.440%	$67.1547	$67.15	$67.15	$67.20
Purchase #5	$175.95	11.748%	$196.6206	$196.62	$196.60	$196.60
Purchase #6	$132.30	11.577%	$147.6164	$147.62	$147.60	$147.60
Purchase #7	$29.27	6.841%	$31.2724	$31.27	$31.25	$31.30
7 purchase totals =	$675.06		$743.5103	$743.51	$743.45	$743.60