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	$87.80	6.820%	$93.788	$93.79	$93.80	$93.80
Purchase #2	$157.75	4.545%	$164.9197	$164.92	$164.90	$164.90
Purchase #3	$47.30	10.859%	$52.4363	$52.44	$52.45	$52.40
Purchase #4	$80.57	10.457%	$88.9952	$89.00	$89.00	$89.00
Purchase #5	$81.90	9.568%	$89.7362	$89.74	$89.75	$89.70
Purchase #6	$227.33	13.606%	$258.2605	$258.26	$258.25	$258.30
Purchase #7	$103.89	12.277%	$116.6446	$116.64	$116.65	$116.60
7 purchase totals =	$786.54		$864.7805	$864.79	$864.80	$864.70