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	$162.32	12.411%	$182.4655	$182.47	$182.45	$182.50
Purchase #2	$40.67	11.783%	$45.4621	$45.46	$45.45	$45.50
Purchase #3	$151.37	13.402%	$171.6566	$171.66	$171.65	$171.70
Purchase #4	$117.66	7.573%	$126.5704	$126.57	$126.55	$126.60
Purchase #5	$99.81	3.122%	$102.9261	$102.93	$102.95	$102.90
Purchase #6	$109.39	12.650%	$123.2278	$123.23	$123.25	$123.20
Purchase #7	$81.30	7.621%	$87.4959	$87.50	$87.50	$87.50
7 purchase totals =	$762.52		$839.8044	$839.82	$839.80	$839.90