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	$212.47	12.332%	$238.6718	$238.67	$238.65	$238.70
Purchase #2	$147.60	8.778%	$160.5563	$160.56	$160.55	$160.60
Purchase #3	$167.59	4.287%	$174.7746	$174.77	$174.75	$174.80
Purchase #4	$205.55	3.175%	$212.0762	$212.08	$212.10	$212.10
Purchase #5	$70.85	13.730%	$80.5777	$80.58	$80.60	$80.60
Purchase #6	$119.66	6.825%	$127.8268	$127.83	$127.85	$127.80
Purchase #7	$37.77	9.642%	$41.4118	$41.41	$41.40	$41.40
7 purchase totals =	$961.49		$1,035.8952	$1,035.90	$1,035.90	$1,036.00