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	$39.58	7.400%	$42.5089	$42.51	$42.50	$42.50
Purchase #2	$156.44	5.436%	$164.9441	$164.94	$164.95	$164.90
Purchase #3	$144.90	10.689%	$160.3884	$160.39	$160.40	$160.40
Purchase #4	$186.90	11.309%	$208.0365	$208.04	$208.05	$208.00
Purchase #5	$168.53	13.256%	$190.8703	$190.87	$190.85	$190.90
Purchase #6	$177.60	10.348%	$195.978	$195.98	$196.00	$196.00
Purchase #7	$145.50	4.217%	$151.6357	$151.64	$151.65	$151.60
7 purchase totals =	$1,019.45		$1,114.3619	$1,114.37	$1,114.40	$1,114.30