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	$11.79	6.695%	$12.5793	$12.58	$12.60	$12.60
Purchase #2	$233.27	9.692%	$255.8785	$255.88	$255.90	$255.90
Purchase #3	$206.69	3.265%	$213.4384	$213.44	$213.45	$213.40
Purchase #4	$41.45	12.259%	$46.5314	$46.53	$46.55	$46.50
Purchase #5	$105.45	8.393%	$114.3004	$114.30	$114.30	$114.30
Purchase #6	$75.82	10.690%	$83.9252	$83.93	$83.95	$83.90
Purchase #7	$212.38	4.874%	$222.7314	$222.73	$222.75	$222.70
7 purchase totals =	$886.85		$949.3846	$949.39	$949.50	$949.30