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	$72.84	13.284%	$82.5161	$82.52	$82.50	$82.50
Purchase #2	$242.42	7.176%	$259.8161	$259.82	$259.80	$259.80
Purchase #3	$213.34	8.530%	$231.5379	$231.54	$231.55	$231.50
Purchase #4	$248.39	3.173%	$256.2714	$256.27	$256.25	$256.30
Purchase #5	$173.94	4.534%	$181.8264	$181.83	$181.85	$181.80
Purchase #6	$90.54	10.205%	$99.7796	$99.78	$99.80	$99.80
Purchase #7	$14.69	3.566%	$15.2138	$15.21	$15.20	$15.20
7 purchase totals =	$1,056.16		$1,126.9613	$1,126.97	$1,126.95	$1,126.90