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	$155.50	8.309%	$168.4205	$168.42	$168.40	$168.40
Purchase #2	$5.83	12.185%	$6.5404	$6.54	$6.55	$6.50
Purchase #3	$232.79	11.521%	$259.6097	$259.61	$259.60	$259.60
Purchase #4	$13.90	9.738%	$15.2536	$15.25	$15.25	$15.30
Purchase #5	$84.45	4.783%	$88.4892	$88.49	$88.50	$88.50
Purchase #6	$181.52	3.393%	$187.679	$187.68	$187.70	$187.70
Purchase #7	$163.35	5.614%	$172.5205	$172.52	$172.50	$172.50
7 purchase totals =	$837.34		$898.5129	$898.51	$898.50	$898.50