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	$121.78	13.280%	$137.9524	$137.95	$137.95	$138.00
Purchase #2	$136.52	4.257%	$142.3317	$142.33	$142.35	$142.30
Purchase #3	$164.88	7.308%	$176.9294	$176.93	$176.95	$176.90
Purchase #4	$59.73	9.417%	$65.3548	$65.35	$65.35	$65.40
Purchase #5	$127.54	3.152%	$131.5601	$131.56	$131.55	$131.60
Purchase #6	$141.77	13.592%	$161.0394	$161.04	$161.05	$161.00
Purchase #7	$127.52	7.751%	$137.4041	$137.40	$137.40	$137.40
7 purchase totals =	$879.74		$952.5719	$952.56	$952.60	$952.60