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	$139.67	5.328%	$147.1116	$147.11	$147.10	$147.10
Purchase #2	$112.79	3.518%	$116.758	$116.76	$116.75	$116.80
Purchase #3	$48.90	10.558%	$54.0629	$54.06	$54.05	$54.10
Purchase #4	$234.27	6.871%	$250.3667	$250.37	$250.35	$250.40
Purchase #5	$201.80	12.715%	$227.4589	$227.46	$227.45	$227.50
Purchase #6	$137.27	13.710%	$156.0897	$156.09	$156.10	$156.10
Purchase #7	$71.65	12.849%	$80.8563	$80.86	$80.85	$80.90
7 purchase totals =	$946.35		$1,032.7041	$1,032.71	$1,032.65	$1,032.90