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	$45.33	12.630%	$51.0552	$51.06	$51.05	$51.10
Purchase #2	$114.65	6.480%	$122.0793	$122.08	$122.10	$122.10
Purchase #3	$56.43	6.214%	$59.9366	$59.94	$59.95	$59.90
Purchase #4	$45.33	13.736%	$51.5565	$51.56	$51.55	$51.60
Purchase #5	$190.29	5.453%	$200.6665	$200.67	$200.65	$200.70
Purchase #6	$24.75	10.280%	$27.2943	$27.29	$27.30	$27.30
Purchase #7	$95.68	9.752%	$105.0107	$105.01	$105.00	$105.00
7 purchase totals =	$572.46		$617.5991	$617.61	$617.60	$617.70