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	$78.90	9.102%	$86.0815	$86.08	$86.10	$86.10
Purchase #2	$18.68	10.841%	$20.7051	$20.71	$20.70	$20.70
Purchase #3	$68.54	6.836%	$73.2254	$73.23	$73.25	$73.20
Purchase #4	$145.56	3.636%	$150.8526	$150.85	$150.85	$150.90
Purchase #5	$152.67	10.269%	$168.3477	$168.35	$168.35	$168.30
Purchase #6	$155.53	13.757%	$176.9263	$176.93	$176.95	$176.90
Purchase #7	$153.96	12.312%	$172.9156	$172.92	$172.90	$172.90
7 purchase totals =	$773.84		$849.0542	$849.07	$849.10	$849.00