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	$156.44	3.162%	$161.3866	$161.39	$161.40	$161.40
Purchase #2	$50.45	5.699%	$53.3251	$53.33	$53.35	$53.30
Purchase #3	$133.39	9.325%	$145.8286	$145.83	$145.85	$145.80
Purchase #4	$99.39	12.166%	$111.4818	$111.48	$111.50	$111.50
Purchase #5	$95.70	9.242%	$104.5446	$104.54	$104.55	$104.50
Purchase #6	$81.66	11.184%	$90.7929	$90.79	$90.80	$90.80
Purchase #7	$203.87	7.868%	$219.9105	$219.91	$219.90	$219.90
7 purchase totals =	$820.90		$887.2701	$887.27	$887.35	$887.20