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	$21.31	3.514%	$22.0588	$22.06	$22.05	$22.10
Purchase #2	$128.96	6.218%	$136.9787	$136.98	$137.00	$137.00
Purchase #3	$156.50	12.212%	$175.6118	$175.61	$175.60	$175.60
Purchase #4	$174.73	4.561%	$182.6994	$182.70	$182.70	$182.70
Purchase #5	$154.32	11.807%	$172.5406	$172.54	$172.55	$172.50
Purchase #6	$9.64	9.497%	$10.5555	$10.56	$10.55	$10.60
Purchase #7	$85.30	12.606%	$96.0529	$96.05	$96.05	$96.10
7 purchase totals =	$730.76		$796.4977	$796.50	$796.50	$796.60