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	$30.59	3.140%	$31.5505	$31.55	$31.55	$31.60
Purchase #2	$170.94	8.559%	$185.5708	$185.57	$185.55	$185.60
Purchase #3	$241.40	7.321%	$259.0729	$259.07	$259.05	$259.10
Purchase #4	$73.25	10.110%	$80.6556	$80.66	$80.65	$80.70
Purchase #5	$36.30	9.430%	$39.7231	$39.72	$39.70	$39.70
Purchase #6	$223.71	11.506%	$249.4501	$249.45	$249.45	$249.50
Purchase #7	$99.83	11.492%	$111.3025	$111.30	$111.30	$111.30
7 purchase totals =	$876.02		$957.3255	$957.32	$957.25	$957.50