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	$138.50	4.113%	$144.1965	$144.20	$144.20	$144.20
Purchase #2	$148.91	12.771%	$167.9273	$167.93	$167.95	$167.90
Purchase #3	$233.28	9.228%	$254.8071	$254.81	$254.80	$254.80
Purchase #4	$143.82	11.801%	$160.7922	$160.79	$160.80	$160.80
Purchase #5	$70.73	13.308%	$80.1427	$80.14	$80.15	$80.10
Purchase #6	$172.98	6.134%	$183.5906	$183.59	$183.60	$183.60
Purchase #7	$80.73	10.691%	$89.3608	$89.36	$89.35	$89.40
7 purchase totals =	$988.95		$1,080.8172	$1,080.82	$1,080.85	$1,080.80