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	$94.47	5.775%	$99.9256	$99.93	$99.95	$99.90
Purchase #2	$103.72	13.675%	$117.9037	$117.90	$117.90	$117.90
Purchase #3	$60.65	6.304%	$64.4734	$64.47	$64.45	$64.50
Purchase #4	$60.80	3.803%	$63.1122	$63.11	$63.10	$63.10
Purchase #5	$142.82	9.857%	$156.8978	$156.90	$156.90	$156.90
Purchase #6	$172.86	10.638%	$191.2488	$191.25	$191.25	$191.20
Purchase #7	$121.92	4.328%	$127.1967	$127.20	$127.20	$127.20
7 purchase totals =	$757.24		$820.7582	$820.76	$820.75	$820.70