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	$80.37	10.211%	$88.5766	$88.58	$88.60	$88.60
Purchase #2	$17.84	5.223%	$18.7718	$18.77	$18.75	$18.80
Purchase #3	$19.40	11.400%	$21.6116	$21.61	$21.60	$21.60
Purchase #4	$148.61	10.374%	$164.0268	$164.03	$164.05	$164.00
Purchase #5	$185.65	3.355%	$191.8786	$191.88	$191.90	$191.90
Purchase #6	$168.47	13.795%	$191.7104	$191.71	$191.70	$191.70
Purchase #7	$231.46	4.710%	$242.3618	$242.36	$242.35	$242.40
7 purchase totals =	$851.80		$918.9376	$918.94	$918.95	$919.00