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	$73.32	6.780%	$78.2911	$78.29	$78.30	$78.30
Purchase #2	$154.43	10.833%	$171.1594	$171.16	$171.15	$171.20
Purchase #3	$149.63	10.226%	$164.9312	$164.93	$164.95	$164.90
Purchase #4	$98.82	7.159%	$105.8945	$105.89	$105.90	$105.90
Purchase #5	$183.99	4.543%	$192.3487	$192.35	$192.35	$192.30
Purchase #6	$5.37	3.824%	$5.5753	$5.58	$5.60	$5.60
Purchase #7	$105.84	9.783%	$116.1943	$116.19	$116.20	$116.20
7 purchase totals =	$771.40		$834.3945	$834.39	$834.45	$834.40