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	$7.50	10.241%	$8.2681	$8.27	$8.25	$8.30
Purchase #2	$144.84	3.864%	$150.4366	$150.44	$150.45	$150.40
Purchase #3	$192.55	4.318%	$200.8643	$200.86	$200.85	$200.90
Purchase #4	$221.50	9.429%	$242.3852	$242.39	$242.40	$242.40
Purchase #5	$166.54	3.830%	$172.9185	$172.92	$172.90	$172.90
Purchase #6	$75.93	12.440%	$85.3757	$85.38	$85.40	$85.40
Purchase #7	$201.93	12.240%	$226.6462	$226.65	$226.65	$226.60
7 purchase totals =	$1,010.79		$1,086.8946	$1,086.91	$1,086.90	$1,086.90