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	$99.56	6.665%	$106.1957	$106.20	$106.20	$106.20
Purchase #2	$35.74	11.738%	$39.9352	$39.94	$39.95	$39.90
Purchase #3	$61.35	10.266%	$67.6482	$67.65	$67.65	$67.60
Purchase #4	$35.63	4.753%	$37.3235	$37.32	$37.30	$37.30
Purchase #5	$172.97	7.275%	$185.5536	$185.55	$185.55	$185.60
Purchase #6	$117.59	3.418%	$121.6092	$121.61	$121.60	$121.60
Purchase #7	$142.63	12.762%	$160.8324	$160.83	$160.85	$160.80
7 purchase totals =	$665.47		$719.0978	$719.10	$719.10	$719.00