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	$5.69	9.826%	$6.2491	$6.25	$6.25	$6.20
Purchase #2	$176.86	5.497%	$186.582	$186.58	$186.60	$186.60
Purchase #3	$219.92	12.550%	$247.52	$247.52	$247.50	$247.50
Purchase #4	$74.86	10.772%	$82.9239	$82.92	$82.90	$82.90
Purchase #5	$194.95	10.341%	$215.1098	$215.11	$215.10	$215.10
Purchase #6	$231.60	10.144%	$255.0935	$255.09	$255.10	$255.10
Purchase #7	$67.80	7.637%	$72.9779	$72.98	$73.00	$73.00
7 purchase totals =	$971.68		$1,066.4562	$1,066.45	$1,066.45	$1,066.40