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	$168.44	13.402%	$191.0143	$191.01	$191.00	$191.00
Purchase #2	$117.38	11.714%	$131.1299	$131.13	$131.15	$131.10
Purchase #3	$137.54	3.300%	$142.0788	$142.08	$142.10	$142.10
Purchase #4	$157.37	4.646%	$164.6814	$164.68	$164.70	$164.70
Purchase #5	$28.27	9.872%	$31.0608	$31.06	$31.05	$31.10
Purchase #6	$77.27	5.821%	$81.7679	$81.77	$81.75	$81.80
Purchase #7	$183.89	4.183%	$191.5821	$191.58	$191.60	$191.60
7 purchase totals =	$870.16		$933.3152	$933.31	$933.35	$933.40