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	$134.43	7.294%	$144.2353	$144.24	$144.25	$144.20
Purchase #2	$182.61	3.250%	$188.5448	$188.54	$188.55	$188.50
Purchase #3	$231.72	11.823%	$259.1163	$259.12	$259.10	$259.10
Purchase #4	$18.89	9.140%	$20.6165	$20.62	$20.60	$20.60
Purchase #5	$135.92	3.854%	$141.1584	$141.16	$141.15	$141.20
Purchase #6	$117.62	7.447%	$126.3792	$126.38	$126.40	$126.40
Purchase #7	$78.78	5.312%	$82.9648	$82.96	$82.95	$83.00
7 purchase totals =	$899.97		$963.0153	$963.02	$963.00	$963.00