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	$28.39	3.776%	$29.462	$29.46	$29.45	$29.50
Purchase #2	$154.51	3.853%	$160.4633	$160.46	$160.45	$160.50
Purchase #3	$134.91	6.200%	$143.2744	$143.27	$143.25	$143.30
Purchase #4	$181.71	4.240%	$189.4145	$189.41	$189.40	$189.40
Purchase #5	$164.83	6.678%	$175.8373	$175.84	$175.85	$175.80
Purchase #6	$138.64	7.310%	$148.7746	$148.77	$148.75	$148.80
Purchase #7	$162.94	3.390%	$168.4637	$168.46	$168.45	$168.50
7 purchase totals =	$965.93		$1,015.6898	$1,015.67	$1,015.60	$1,015.80