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	$146.63	12.461%	$164.9016	$164.90	$164.90	$164.90
Purchase #2	$94.89	4.869%	$99.5102	$99.51	$99.50	$99.50
Purchase #3	$162.49	10.426%	$179.4312	$179.43	$179.45	$179.40
Purchase #4	$182.49	13.523%	$207.1681	$207.17	$207.15	$207.20
Purchase #5	$137.79	4.791%	$144.3915	$144.39	$144.40	$144.40
Purchase #6	$41.36	11.442%	$46.0924	$46.09	$46.10	$46.10
Purchase #7	$142.25	4.524%	$148.6854	$148.69	$148.70	$148.70
7 purchase totals =	$907.90		$990.1804	$990.18	$990.20	$990.20