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	$39.84	3.239%	$41.1304	$41.13	$41.15	$41.10
Purchase #2	$215.90	5.717%	$228.243	$228.24	$228.25	$228.20
Purchase #3	$120.65	10.302%	$133.0794	$133.08	$133.10	$133.10
Purchase #4	$35.93	4.712%	$37.623	$37.62	$37.60	$37.60
Purchase #5	$33.35	12.492%	$37.5161	$37.52	$37.50	$37.50
Purchase #6	$58.25	5.296%	$61.3349	$61.33	$61.35	$61.30
Purchase #7	$218.50	9.364%	$238.9603	$238.96	$238.95	$239.00
7 purchase totals =	$722.42		$777.8871	$777.88	$777.90	$777.80