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	$6.45	5.800%	$6.8241	$6.82	$6.80	$6.80
Purchase #2	$73.93	11.221%	$82.2257	$82.23	$82.25	$82.20
Purchase #3	$127.79	13.280%	$144.7605	$144.76	$144.75	$144.80
Purchase #4	$135.87	5.831%	$143.7926	$143.79	$143.80	$143.80
Purchase #5	$248.58	3.299%	$256.7807	$256.78	$256.80	$256.80
Purchase #6	$206.74	10.551%	$228.5531	$228.55	$228.55	$228.60
Purchase #7	$141.30	3.223%	$145.8541	$145.85	$145.85	$145.90
7 purchase totals =	$940.66		$1,008.7908	$1,008.78	$1,008.80	$1,008.90