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	$127.58	9.185%	$139.2982	$139.30	$139.30	$139.30
Purchase #2	$145.60	11.752%	$162.7109	$162.71	$162.70	$162.70
Purchase #3	$40.41	6.250%	$42.9356	$42.94	$42.95	$42.90
Purchase #4	$233.54	8.582%	$253.5824	$253.58	$253.60	$253.60
Purchase #5	$13.39	7.783%	$14.4321	$14.43	$14.45	$14.40
Purchase #6	$130.72	4.447%	$136.5331	$136.53	$136.55	$136.50
Purchase #7	$211.29	4.155%	$220.0691	$220.07	$220.05	$220.10
7 purchase totals =	$902.53		$969.5614	$969.56	$969.60	$969.50