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	$26.97	4.870%	$28.2834	$28.28	$28.30	$28.30
Purchase #2	$213.79	13.830%	$243.3572	$243.36	$243.35	$243.40
Purchase #3	$176.90	11.147%	$196.619	$196.62	$196.60	$196.60
Purchase #4	$248.79	13.552%	$282.506	$282.51	$282.50	$282.50
Purchase #5	$51.45	3.731%	$53.3696	$53.37	$53.35	$53.40
Purchase #6	$28.68	6.712%	$30.605	$30.61	$30.60	$30.60
Purchase #7	$230.85	10.667%	$255.4748	$255.47	$255.45	$255.50
7 purchase totals =	$977.43		$1,090.2150	$1,090.22	$1,090.15	$1,090.30