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	$87.63	3.288%	$90.5113	$90.51	$90.50	$90.50
Purchase #2	$214.59	3.255%	$221.5749	$221.57	$221.55	$221.60
Purchase #3	$152.84	12.509%	$171.9588	$171.96	$171.95	$172.00
Purchase #4	$76.90	9.190%	$83.9671	$83.97	$83.95	$84.00
Purchase #5	$21.48	13.571%	$24.3951	$24.40	$24.40	$24.40
Purchase #6	$212.77	9.108%	$232.1491	$232.15	$232.15	$232.10
Purchase #7	$171.83	3.827%	$178.4059	$178.41	$178.40	$178.40
7 purchase totals =	$938.04		$1,002.9622	$1,002.97	$1,002.90	$1,003.00