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	$127.76	7.803%	$137.7291	$137.73	$137.75	$137.70
Purchase #2	$215.37	3.183%	$222.2252	$222.23	$222.25	$222.20
Purchase #3	$175.47	6.671%	$187.1756	$187.18	$187.20	$187.20
Purchase #4	$177.32	7.473%	$190.5711	$190.57	$190.55	$190.60
Purchase #5	$178.84	11.444%	$199.3064	$199.31	$199.30	$199.30
Purchase #6	$19.60	9.477%	$21.4575	$21.46	$21.45	$21.50
Purchase #7	$243.76	5.392%	$256.9035	$256.90	$256.90	$256.90
7 purchase totals =	$1,138.12		$1,215.3684	$1,215.38	$1,215.40	$1,215.40