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	$144.31	8.594%	$156.712	$156.71	$156.70	$156.70
Purchase #2	$153.66	7.127%	$164.6113	$164.61	$164.60	$164.60
Purchase #3	$245.73	9.858%	$269.9541	$269.95	$269.95	$270.00
Purchase #4	$9.41	10.104%	$10.3608	$10.36	$10.35	$10.40
Purchase #5	$133.39	5.134%	$140.2382	$140.24	$140.25	$140.20
Purchase #6	$188.25	3.376%	$194.6053	$194.61	$194.60	$194.60
Purchase #7	$196.42	6.845%	$209.8649	$209.86	$209.85	$209.90
7 purchase totals =	$1,071.17		$1,146.3466	$1,146.34	$1,146.30	$1,146.40