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	$86.55	5.175%	$91.029	$91.03	$91.05	$91.00
Purchase #2	$166.42	6.227%	$176.783	$176.78	$176.80	$176.80
Purchase #3	$95.38	5.448%	$100.5763	$100.58	$100.60	$100.60
Purchase #4	$160.43	9.635%	$175.8874	$175.89	$175.90	$175.90
Purchase #5	$245.57	6.401%	$261.2889	$261.29	$261.30	$261.30
Purchase #6	$109.92	3.629%	$113.909	$113.91	$113.90	$113.90
Purchase #7	$69.35	12.442%	$77.9785	$77.98	$78.00	$78.00
7 purchase totals =	$933.62		$997.4521	$997.46	$997.55	$997.50