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	$83.53	7.760%	$90.0119	$90.01	$90.00	$90.00
Purchase #2	$178.61	10.208%	$196.8425	$196.84	$196.85	$196.80
Purchase #3	$22.42	9.289%	$24.5026	$24.50	$24.50	$24.50
Purchase #4	$88.42	11.229%	$98.3487	$98.35	$98.35	$98.30
Purchase #5	$227.74	3.453%	$235.6039	$235.60	$235.60	$235.60
Purchase #6	$138.60	6.857%	$148.1038	$148.10	$148.10	$148.10
Purchase #7	$161.45	3.858%	$167.6787	$167.68	$167.70	$167.70
7 purchase totals =	$900.77		$961.0921	$961.08	$961.10	$961.00