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	$204.60	12.120%	$229.3975	$229.40	$229.40	$229.40
Purchase #2	$213.92	12.768%	$241.2333	$241.23	$241.25	$241.20
Purchase #3	$73.62	11.817%	$82.3197	$82.32	$82.30	$82.30
Purchase #4	$158.51	8.555%	$172.0705	$172.07	$172.05	$172.10
Purchase #5	$70.56	3.224%	$72.8349	$72.83	$72.85	$72.80
Purchase #6	$199.98	9.807%	$219.592	$219.59	$219.60	$219.60
Purchase #7	$183.89	5.259%	$193.5608	$193.56	$193.55	$193.60
7 purchase totals =	$1,105.08		$1,211.0087	$1,211.00	$1,211.00	$1,211.00