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	$170.76	9.847%	$187.5747	$187.57	$187.55	$187.60
Purchase #2	$25.59	13.644%	$29.0815	$29.08	$29.10	$29.10
Purchase #3	$164.88	13.634%	$187.3597	$187.36	$187.35	$187.40
Purchase #4	$96.73	7.272%	$103.7642	$103.76	$103.75	$103.80
Purchase #5	$215.87	9.598%	$236.5892	$236.59	$236.60	$236.60
Purchase #6	$13.98	11.527%	$15.5915	$15.59	$15.60	$15.60
Purchase #7	$229.88	4.555%	$240.351	$240.35	$240.35	$240.40
7 purchase totals =	$917.69		$1,000.3118	$1,000.30	$1,000.30	$1,000.50