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	$188.97	10.286%	$208.4075	$208.41	$208.40	$208.40
Purchase #2	$49.91	13.148%	$56.4722	$56.47	$56.45	$56.50
Purchase #3	$23.32	13.816%	$26.5419	$26.54	$26.55	$26.50
Purchase #4	$226.49	5.468%	$238.8745	$238.87	$238.85	$238.90
Purchase #5	$36.86	9.383%	$40.3186	$40.32	$40.30	$40.30
Purchase #6	$62.90	4.163%	$65.5185	$65.52	$65.50	$65.50
Purchase #7	$241.59	10.662%	$267.3483	$267.35	$267.35	$267.30
7 purchase totals =	$830.04		$903.4815	$903.48	$903.40	$903.40