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	$231.61	10.217%	$255.2736	$255.27	$255.25	$255.30
Purchase #2	$41.50	4.496%	$43.3658	$43.37	$43.35	$43.40
Purchase #3	$93.33	7.127%	$99.9816	$99.98	$100.00	$100.00
Purchase #4	$44.68	10.409%	$49.3307	$49.33	$49.35	$49.30
Purchase #5	$248.47	5.219%	$261.4376	$261.44	$261.45	$261.40
Purchase #6	$125.93	4.156%	$131.1637	$131.16	$131.15	$131.20
Purchase #7	$161.79	6.838%	$172.8532	$172.85	$172.85	$172.90
7 purchase totals =	$947.31		$1,013.4062	$1,013.40	$1,013.40	$1,013.50