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	$92.67	8.464%	$100.5136	$100.51	$100.50	$100.50
Purchase #2	$226.49	9.850%	$248.7993	$248.80	$248.80	$248.80
Purchase #3	$232.68	7.775%	$250.7709	$250.77	$250.75	$250.80
Purchase #4	$59.42	12.402%	$66.7893	$66.79	$66.80	$66.80
Purchase #5	$239.43	6.778%	$255.6586	$255.66	$255.65	$255.70
Purchase #6	$61.49	6.254%	$65.3356	$65.34	$65.35	$65.30
Purchase #7	$207.67	12.809%	$234.2705	$234.27	$234.25	$234.30
7 purchase totals =	$1,119.85		$1,222.1378	$1,222.14	$1,222.10	$1,222.20