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	$60.69	5.595%	$64.0856	$64.09	$64.10	$64.10
Purchase #2	$146.27	12.397%	$164.4031	$164.40	$164.40	$164.40
Purchase #3	$182.91	12.306%	$205.4189	$205.42	$205.40	$205.40
Purchase #4	$72.82	13.568%	$82.7002	$82.70	$82.70	$82.70
Purchase #5	$168.85	6.372%	$179.6091	$179.61	$179.60	$179.60
Purchase #6	$18.36	11.513%	$20.4738	$20.47	$20.45	$20.50
Purchase #7	$131.37	6.737%	$140.2204	$140.22	$140.20	$140.20
7 purchase totals =	$781.27		$856.9111	$856.91	$856.85	$856.90