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	$210.78	13.519%	$239.2753	$239.28	$239.30	$239.30
Purchase #2	$100.63	6.871%	$107.5443	$107.54	$107.55	$107.50
Purchase #3	$85.90	4.683%	$89.9227	$89.92	$89.90	$89.90
Purchase #4	$57.93	6.156%	$61.4962	$61.50	$61.50	$61.50
Purchase #5	$226.79	4.805%	$237.6873	$237.69	$237.70	$237.70
Purchase #6	$133.69	3.450%	$138.3023	$138.30	$138.30	$138.30
Purchase #7	$186.99	4.820%	$196.0029	$196.00	$196.00	$196.00
7 purchase totals =	$1,002.71		$1,070.2310	$1,070.23	$1,070.25	$1,070.20