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	$241.26	13.122%	$272.9181	$272.92	$272.90	$272.90
Purchase #2	$154.91	11.398%	$172.5666	$172.57	$172.55	$172.60
Purchase #3	$119.57	7.661%	$128.7303	$128.73	$128.75	$128.70
Purchase #4	$83.36	9.761%	$91.4968	$91.50	$91.50	$91.50
Purchase #5	$97.27	4.735%	$101.8757	$101.88	$101.90	$101.90
Purchase #6	$200.87	10.654%	$222.2707	$222.27	$222.25	$222.30
Purchase #7	$136.92	3.615%	$141.8697	$141.87	$141.85	$141.90
7 purchase totals =	$1,034.16		$1,131.7279	$1,131.74	$1,131.70	$1,131.80