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	$154.83	6.120%	$164.3056	$164.31	$164.30	$164.30
Purchase #2	$101.65	10.778%	$112.6058	$112.61	$112.60	$112.60
Purchase #3	$236.78	5.583%	$249.9994	$250.00	$250.00	$250.00
Purchase #4	$135.83	3.590%	$140.7063	$140.71	$140.70	$140.70
Purchase #5	$52.39	4.635%	$54.8183	$54.82	$54.80	$54.80
Purchase #6	$172.92	10.669%	$191.3688	$191.37	$191.35	$191.40
Purchase #7	$245.27	8.220%	$265.4312	$265.43	$265.45	$265.40
7 purchase totals =	$1,099.67		$1,179.2354	$1,179.25	$1,179.20	$1,179.20